Tumors of the Liver, Gallbladder, and Biliary Tree

Clinical Features.

Hepatocellular adenomas (HCAs) historically have been seen mostly in younger women during their reproductive years but are rare in men and children. In recent years, however, HCAs have developed in an increasing number of older women as well as men, correlating with the recognition of different histologic subtypes of adenoma (see later discussion). Most HCAs occur in histologically normal or nearly normal liver, and multiple HCAs within the liver are becoming more commonly recognized. By convention, the term hepatic adenomatosis is used when more than 10 adenomas are present.

The clinical presentation is generally that of an abdominal mass, but some patients also have abdominal pain, discomfort, or nausea. Rupture and hemorrhage with hemoperitoneum can occur with larger tumors. Serum alkaline phosphatase level may be elevated, but serum α-fetoprotein (AFP) levels are generally normal or minimally elevated. HCAs historically have been associated with the long-term use of oral contraceptives: Most patients have used them for more than 5 years before diagnosis. Other related agents such as anabolic steroids, clomiphene, danazol, and carbamazepine have also been associated with HCA. Now, with the recognition of HCA subtypes occurring in older women and in men, additional other risk factors such as diabetes mellitus and obesity, as well as a familial association, have been recognized. Other associations include Klinefelter syndrome and metabolic disorders such as glycogen storage diseases I and III, galactosemia, and tyrosinemia. In rare instances, HCAs have been observed in association with severe combined immunodeficiency, familial adenomatous polyposis, and congenital or acquired vascular flow abnormalities in the liver. Several cases of primary liver cell adenoma of the placenta have also been described. The diagnosis of HCA should be made with caution in the absence of hormonal or metabolic etiologies, as they may represent well-differentiated hepatocellular carcinoma (HCC). It has been suggested that these patients should be investigated for abnormal secretion of sex steroids. The International Working Party had recommended that the diagnosis of HCA should not be made in a cirrhotic liver, unless evidence exists of regression when the stimulus is removed or one of the previously mentioned risk factors is present. More recently, HCAs of the inflammatory subtype have been described in cirrhotic liver. HCA appears as a hyperdense heterogenous tumor on computed tomography (CT) occasionally with central hemorrhage, and does not show uptake on technetium scintigraphy. An accuracy of 75% has been reported in subtyping of HCAs by magnetic resonance imaging (MRI) using liver-specific contrast agents. However, the distinction of HCA and HCC is often not possible based on imaging.

Pathologic Features and Subclassification

Gross Pathology.

HCAs tend to bulge on cut section, but the appearance may vary if necrosis or hemorrhage is present. Extensive fatty change can lead to a pale appearance, while a mottled dark appearance may result from necrosis and hemorrhage ( Fig. 10.1 ). The size can be extremely variable. The tumor may or may not be encapsulated; if a capsule is present, it is often incomplete. HCA generally lacks significant fibrosis or nodularity, but these features may be present following hemorrhage and infarction. Less commonly, adenomas may be bile stained or have a slate gray to black color due to the presence of large amounts of lipofuscin pigment, the so-called black adenoma. All tumors are highly vascular, and those associated with anabolic or androgenic steroids may also show macroscopic peliosis.

Microscopic Features Common to All Subtypes.

HCAs are composed of a relatively uniform population of hepatocytes arranged in plates that are one to three cells thick. The cell plates are usually more irregular and nonlinear than in the normal liver. The reticulin framework of the cell plates is intact ( Fig. 10.2 ) and similar to that in normal liver, or only focally decreased. The tumor cells are usually the same size as normal hepatocytes or slightly smaller, with a normal nuclear to cytoplasmic ratio. The cytoplasm may be eosinophilic or clear and contain fat, bile, or lipofuscin pigment ( Fig. 10.3 ). Periodic acid–Schiff (PAS)–positive diastase-resistant globules, giant mitochondria, and Mallory-Denk bodies may be noted but are not prominent. Other occasional variations in cellular morphology include multinucleation, focal atypia, and nuclear pleomorphism. Regardless of the cellular morphology, mitotic figures are absent or extremely rare. Variations in architecture such as the formation of small acini (pseudoglands [i.e., glandlike structures composed of hepatocytes]) can be found, but are typically not prominent; such acinar structures can contain bile. Alterations in the sinusoids can also be present; they may appear compressed, resulting in a somewhat uniform, solid appearance to the tumor, or, alternatively, sinusoidal dilatation ( Fig. 10.4 ) or peliosis hepatis may be present. Large vessels are often quite prominent. Areas of infarction and hemorrhage are frequent findings. Organization of these foci can lead to fibrous scars. Kupffer cells may be seen but tend to be fewer in number than in normal liver. HCAs associated with anabolic steroids (the β-catenin–mutated type; see later discussion) are more likely to show nuclear atypia, prominent nucleoli, peliosis hepatis, or a prominent acinar (pseudoglandular) pattern. By definition, portal zones are absent, and ductular reaction is typically not present except in the inflammatory variant. The presence of arterioles without accompanying bile ducts and surrounded by scant connective tissue is a characteristic feature of HCA (“naked” arterioles) but is not diagnostic as it can also be seen in focal nodular hyperplasia (FNH) and HCC.

Immunohistochemistry.

HCA is positive for hepatocellular markers, including arginase-1, hepatocyte antibody (Hep Par l), and polyclonal carcinoembryonic antigen (CEA) in a canalicular pattern similar to normal liver. HCA shows increased sinusoidal staining with CD34 ( Fig. 10.5 ), similar to that seen in FNH and HCC. AFP is negative in HCA. Other immunohistochemical findings such as positive cytoplasmic staining for serum amyloid A (SAA), C-reactive protein (CRP), glutamine synthetase (GS), nuclear positivity for β-catenin, and absence of liver fatty acid binding protein (LFABP) can be useful to identify specific subtypes (see later).

Pathologic Classification.

The World Health Organization (WHO) 2010 classification recognizes four subgroups of HCA.

Hepatocyte Nuclear Factor-1α (HNF1α)-Inactivated HCA (HHCA).

This variant occurs as a result of either somatic or germline mutations in HNF1α. The HHCA typically shows diffuse fatty change (see Fig. 10.3 ). These lesions demonstrate a complete absence of LFABP on immunostaining. HHCA occurs almost exclusively in women, and small adenomas of this type can be mistaken for focal fatty change. The reticulin framework in these lesions typically demonstrates small packets of hepatocytic tumor cells (rounded small clusters) surrounded by reticulin ( Fig. 10.6 ). This subtype has very low risk for malignancy.

β-Catenin-Activated HCA (BHCA).

This variant shows β-catenin activation and upregulation of glutamine synthetase, as evidenced by positive nuclear immunostaining for β-catenin and/or diffuse cytoplasmic immunostaining for GS. Diffuse GS staining is defined by moderate to strong cytoplasmic staining in more than 50% of lesional hepatocytes. It can be diffuse homogeneous when nearly all the tumor cells are positive ( Fig. 10.7 ) or diffuse heterogeneous when staining is seen in more than 50% but not all of the lesional cells ( Fig. 10.8 ). This subtype is usually solitary and often associated with male hormone use and glycogenosis. This variant has a high risk for concurrent or subsequent HCC. Cytologic atypia and architectural changes such as pseudoacinar formation are frequent in this variant.

Inflammatory HCA (IHCA).

This form accounts for more than 50% of HCAs and can be single or multiple. IHCA has also been known as telangiectatic HCA and was previously considered to be a telangiectatic form of FNH. This variant is characterized by activation of the interleukin (IL)–6 signaling pathway, most commonly due to mutation in the IL6ST gene that encodes the signaling coreceptor gp130. Most IHCAs occur in women and are frequently associated with obesity, fatty liver, and/or the metabolic syndrome. This form is now being increasingly recognized in men with similar risk factors. Prominent sinusoidal dilation (see Fig. 10.4 ) and an inflammatory infiltrate, usually lymphocytic, are typical histologic features. Fibrous septa and ductular reaction are variably prominent and can mimic FNH.

Immunohistochemically it shows expression of inflammatory markers such as serum amyloid–associated protein and C-reactive protein ( Fig. 10.9 ). Both SAA and CRP can also stain adjacent nonneoplastic liver parenchyma. SAA is positive in more than 90% of IHCA and is more specific compared to CRP, which is positive in nearly all IHCA, but is also more commonly positive in adjacent liver and FNH.

Unclassified HCA (UHCA).

These tumors have typical features of HCAs but lack specific histologic features or known mutations. These are estimated to constitute less than 10% of HCAs.

Differential Diagnosis

• a.

  Normal liver: Presence of unpaired arterioles and absence of portal tracts point toward a neoplastic lesion, but distinction of HCA and normal liver may be difficult in small biopsies or cell blocks. Diffuse sinusoidal staining with CD34 and patchy GS staining beyond the pericentral region help in distinguishing a mass lesion from normal parenchyma.

• b.

  FNH: The presence of fibrous septa, nodular architecture, and ductular reaction is more typical of FNH. Large vessels with abnormal hyperplastic features and surrounded by connective tissue as well as presence of central scar favor FNH. The larger vessels in HCA tend to have a more normal configuration and lack significant perivascular connective tissue stroma. However, there is overlap in the histologic features of FNH and inflammatory HCA, and the distinction can be challenging on needle biopsies. Pseudoglandular differentiation in some adenomas can also be mistaken for bile ductules. Immunohistochemistry plays an important role in the diagnosis as positive staining with SAA and CRP is characteristic of IHCA. Focal SAA staining can be seen in a small subset of FNH, while periseptal staining with CRP is common in FNH. Maplike GS staining is diagnostic of FNH (see later discussion) and is not observed in IHCA.

• c.

  HCC: Histologic features such as small cell change, thick cell plates, cytologic atypia, prominent pseudoacinar change, and/or multifocal reticulin loss help in distinguishing HCC from HCA ( Table 10.1 ). Diffuse sinusoidal CD34 staining can be seen on both HCA and HCC. A combination of glypican-3 (GPC3), GS, and heat shock protein 70 (HSP70) has been advocated for distinguishing HCA and HCC. GPC3, an oncofecal antigen, is positive in around 50% of well-differentiated HCC but negative in HCC. Diffuse GS indicates β-activation and is more often seen in HCC. HSP70 is overexpressed in HCC and is negative in HCA. Of these three stains, diffuse GS is most helpful as it points toward HCC or high-risk β-activated HCA. GPC3 and HSP70 are less useful as most cases that are positive for one or both markers can be diagnosed as HCC based on morphology and reticulin stain. Cytogenetic changes such as gains of chromosomes 1 and 8 are common in HCC (see Table 10.1 ), but are not observed in HCA. Similarly, TERT promoter mutations are seen in HCC but not in typical HCA. These tests are promising, but are not currently available for clinical use.

  TABLE 10.1

  Distinction Among Focal Nodular Hyperplasia, Hepatocellular Adenoma, and Hepatocellular Carcinoma.

  	Focal Nodular Hyperplasia	Hepatocellular Adenoma	Hepatocellular Carcinoma
  Clinical Features
  Age; sex	All ages; most common in young women, can occur in men	Mostly women in third or fourth decade; men: Infl and β-catenin types	Most common in men (3×)
  Oral contraceptive use	Occasional	Common	Generally absent
  Male hormone use	None	Only in β-catenin variant	Rare reports
  Other features	Association with vascular problems or cavernous hemangioma	Obesity, alcohol, diabetes mellitus	Chronic liver disease/cirrhosis of diverse etiologies
  Background liver	Normal	Normal, or with fatty change (resulting from obesity)	Cirrhosis (>80%)
  α-Fetoprotein	Normal	Normal	Often elevated; can be normal, especially in small tumors
  Radiology	Homogeneous enhancement on CT and MRI. Normal or increased uptake on scintigraphy. Hypovascular on angiography	Heterogeneous mass on CT and MRI. Decreased uptake on scintigraphy. Hypervascular on angiography	Arterial phase enhancement on CT and MRI with contrast. Highly vascular on angiography
  Morphologic Features
  Capsule	Absent	May be present	May be present
  Number	Usually solitary, sometimes multiple	Solitary or multiple Adenomatosis >10	Solitary or multiple
  Central scar	Present	Absent	Absent
  Hemorrhage or necrosis	Rare	Common in larger tumors	Common in larger tumors
  Parenchyma	Nodular with fibrous septa	Homogeneous	Nodular or homogeneous
  Bile	Usually absent	Can be present	Can be present
  Steatosis	Variable, usually not prominent	Most prominent in HNFα1 variant	Variable
  Bile ductular reaction	Present, usually prominent	Present in Infl HCA	Absent
  Interlobular bile ducts	Absent except at periphery	Absent except at periphery	Absent
  Vessels	Aberrant arterioles with myointimal thickening present in fibrous stroma	“Naked” arterioles without bile ducts accompanied by scant stroma; arterioles in clusters in Infl HCA	“Naked” arterioles without bile ducts accompanied by scant stroma
  Cell plates	One to three cells thick, rarely up to five cells	One to three cells thick	Usually more than three cells thick
  Kupffer cells	Present	Reduced or absent	Absent
  Nuclear atypia	Typically not present, but can occur	Absent or minimal	Often present
  Nucleus to cytoplasm ratio	Normal	Normal	Increased
  Nucleoli	Variable	Variable	Often prominent
  Mitoses	Absent	Absent	Often present
  Reticulin	Normal, possible more prominent	Normal to mild variability with acinar-like pattern	Often decreased or absent; or highlights atypical architecture
  Immunohistochemistry
  CD34+ endothelium along cell plates or sinusoids	Can be positive, usually patchy	Often positive, patchy or diffuse	Typically positive to variable extent
  Glutamine synthetase	Maplike pattern	Variable, usually some perivenous staining	Variable
  Serum amyloid A	Focal, scant to absent	Positive in Infl HCA	Usually absent
  β-Catenin nuclear positivity	Absent	Positive with the β-catenin mutation, including some Infl HCA	Positive in 10% with the β-catenin mutation
  Molecular Techniques
  Clonality	Polyclonal (some variants can be monoclonal)	Monoclonal	Monoclonal
  FISH, CGH	Not known	Normal or minimal abnormalities	Characteristic chromosomal changes (gains of 1q, 7q, 8q; loss of 16q)
  TERT promoter mutation	Absent	Absent	Present in around 60% of cases

  CGH, Comparative genomic hybridization; CT, computed tomography; FISH, fluorescence in situ hybridization; HNFα1, hepatocyte nuclear factor; Infl HCA, inflammatory variant of hepatocellular adenoma; MRI, magnetic resonance imaging.

• d.

  Atypical hepatocellular neoplasms: In some instances, distinction between HCA and HCC is not possible. The terms atypical hepatocellular neoplasm or hepatocellular neoplasm with uncertain malignant potential (HUMP) have been advocated for these borderline tumors. Although there are no widely accepted guidelines for use of this terminology, its use has been suggested for (i) clinically atypical setting such as male gender and older age (>50 years), especially in needle biopies; (ii) atypical morphologic features such as small cell change, pseudoacinar architecture, and reticulin loss that is insufficient for a definite diagnosis of HCC; and (iii) β-catenin activated tumors since these are high-risk tumors even in the absence of unequivocal features of HCC. If there is sufficient cytoarchitectural atypia and/or multifocal reticulin loss, the diagnosis of HCC should be rendered.

Prognosis and Outcome.

Some HCAs associated with oral contraceptives regress after withdrawal of the drugs, but the majority do not. Rarely, HCCs have been found arising within HCA, a phenomenon that is most commonly seen with β-catenin–activated HCA. Some authors have also reported an increased risk of progression in pigmented adenomas. The risk of HCC developing in an HCA may otherwise be low, but surgical resection has been advocated in all cases in view of the potentially fatal complication of rupture and hemoperitoneum. Management of adenomatosis, which is now by consensus considered to consist of greater than 10 HCAs, can be challenging because of the high risk of hemorrhage, and liver transplantation may be necessary because of the unresectable nature of numerous parenchymal lesions.

Hepatic Adenomatosis.

Multiple HCAs can occur in the hereditary or sporadic setting and are termed adenomatosis if there are 10 or more HCAs. In the hereditary setting, it is most often related to germline mutations in HNF1α and can be associated with maturity-onset diabetes of the young type 3. In the sporadic setting, adenomatosis is usually related to metabolic risk factors, and most often comprises the HHCA or IHCA subtypes. Multiple HCAs can also occur in the setting of vascular diseases such as Budd-Chiari syndrome and congenital absence of portal vein. The risk for HCC is highest with larger tumors (>5 cm) and those with β-catenin activation similar to sporadic HCA. Hence resection of larger tumors is recommended. If the tumors are unresectable, embolization or transplantation has been tried.

Clinical Features.

FNH is a benign nonneoplastic lesion, most commonly seen in young women in the third and fourth decades. Around 5% to 15% of the lesions occur in men, which is a higher proportion compared with HCA. FNH is often noted as an incidental finding at surgery or during radiologic tests for an unrelated disease but may also present with upper abdominal pain or, rarely, with complications such as hemorrhage due to large size. Liver function tests are generally normal, but some patients may have elevated γ-glutamyl transpeptidase activity.

FNH is usually a solitary lesion; multifocal lesions have been reported in 20% to 30% of cases. FNH has been described adjacent to hemangiomas, the association being more common with multiple FNH. Some patients with the so-called multiple FNH syndrome have at least two FNH lesions associated with one or more lesions such as hepatic cavernous hemangioma, systemic arterial structural defects such as Klippel-Trénaunay-Weber syndrome, and cerebral aneurysms, meningioma, and astrocytoma. Unlike HCA, FNH is not thought to develop as a result of oral contraceptives, but many speculate that it may increase in size with their use or regress with their cessation. The currently favored hypothesis is that FNH represents a hyperplastic and altered growth response to changes in blood flow in the parenchyma, perhaps surrounding a preexisting arteriovenous malformation or arteriovenous shunt. The presence of numerous abnormal muscular vessels and the association with hemangiomas and the Budd-Chiari syndrome lend support to this theory. Aberrant expression of angiopoietin genes occurs in FNH and may play a role in the formation of hyperplastic and dystrophic vessels. FNH-like lesions associated with the Budd-Chiari syndrome and Osler-Weber-Rendu disease probably should not be designated as FNH, but rather referred to as either regenerative nodules or FNH-like lesions. Most data demonstrate polyclonality in FNH, favoring a reactive process rather than a neoplasm.

Pathologic Features

Gross Pathology.

FNH has a nodular appearance (which can suggest the appearance of macronodular cirrhosis) and tends to be lighter brown than the adjacent liver ( Fig. 10.10 ). These lesions are often located near the capsule of the liver and can occasionally be pedunculated. The edges of FNH appear well demarcated from the adjacent normal parenchyma because of the nodularity, but no fibrous capsule is present. Most lesions are less than 5 cm, but considerable variation is seen in size, and an entire lobe can be involved in rare instances. Most of the lesions have a central fibrous scar, which consists of fibrovascular tissue rather than dense collagen. The central scar may be absent, particularly in lesions less than 1 cm.

Microscopic Features.

FNH is composed of normal-appearing hepatocytes arranged in complete or incomplete nodules that are separated by fibrous tissue, which tends to extend from the central fibrous zone. The cell plate architecture has an intact reticulin framework similar to that of normal liver, but the cell plates are usually wider (two to three cells thick), as in a regenerative nodule, and rarely can even be wider than three cells. The hepatocytes may show increased cytoplasmic glycogen, focal steatosis, bile stasis, lipofuscin, iron pigment, copper-associated protein, and Mallory-Denk bodies. Foci of atypical hepatocytes with large nuclei, mild nuclear hyperchromasia, and conspicuous nucleoli can be present. Cytologic atypia of the large cell type has been described rarely. An important feature is the variable number of bile ductular structures present within the fibrous stroma at the edge of the nodules ( Fig. 10.11 ). Another important diagnostic feature is the presence of medium to large thick-walled muscular vessels, which often exhibit myointimal myxoid or fibromuscular hyperplastic changes. These vessels are not a component of a portal tract as no portal vein or interlobular duct of similar caliber is associated with them. Normal portal tracts are typically not found within the lesion, but can be seen near the edge of the lesion, and a bile duct of intermediate or large caliber can be found in the central fibrous zone in rare cases. Sinusoids can be somewhat dilated, and Kupffer cells can be present. Inflammatory cell infiltrates are relatively common in the fibrous septa and generally consist of lymphocytes, although neutrophils and eosinophils can be noted, especially around the bile ductular structures. Rarely, granulomas may be seen.

Immunohistochemistry.

The hepatocytes in FNH express hepatocellular markers such as Hep Par 1, CAM5.2, and polyclonal CEA. A sinusoidal pattern of staining with CD34 is present, which can be patchy or diffuse. AFP is always negative. GS immunohistochemistry in FNH shows a highly characteristic geographic or maplike pattern characterized by strong cytoplasmic staining in broad groups of hepatocytes that are interconnected, while small areas around the fibrous septa tend to be negative ( Fig. 10.12 ). In contrast, this enzyme is confined to the hepatocytes in zone 3 in normal liver. Use of CK7 staining may help to identify a ductular reaction in FNH.

Differential Diagnosis.

FNH needs to be distinguished from normal liver, HCA, regenerative nodules, and HCC (see Table 10.1 ). Absence of normal portal tracts, maplike staining with GS, and increased sinusoidal staining with CD34 can help distinguish FNH from normal liver. Entrapped portal tracts can occasionally be seen at the edge of FNH, a finding that can also occur in HCA and HCC. FNH typically shows homogeneous enhancement with a central scar on CT and MRI, whereas HCA appears as a hyperintense heterogeneous mass. FNH shows normal or increased uptake on Tc-sulfur-colloid scintigraphy; HCA appears as a lesion without uptake. The use of MRI with liver-specific contrast agents greatly increases the accuracy of diagnosis of FNH, but the radiologic findings can overlap with inflammatory HCA. The combination of histologic and immunohistochemical features can distinguish FNH from HCA in most cases (see HCA section).

Regenerative nodules associated with Budd-Chiari syndrome and vascular malformations resemble FNH and have been designated as FNH-like lesions. ^l Likewise, lesions similar to FNH also can be seen in cirrhotic liver. Most FNH-like lesions show GS maplike staining, but some cases may lack this characteristic pattern of staining. Most FNHs and some fibrolamellar HCCs have a central scar and can be confused on radiologic studies. The presence of calcification in the scar favors fibrolamellar HCC, although it has occasionally been reported in FNH. Some of the typical features of FNH, such as nodular architecture with fibrosis, bile ductular reaction, and absence of interlobular bile ducts, can closely resemble chronic ductopenic biliary disease, especially on a limited biopsy. Clinical information of normal liver enzymes, radiologic findings of a focal mass lesion, and maplike GS staining are helpful in the diagnosis of FNH in this setting.

Prognosis and Outcome.

FNH is a benign lesion and, in contrast to HCA, the risk of complications such as hemorrhage and malignant transformation is virtually absent. In spite of its rarely reported association with fibrolamellar HCC, no real evidence exists for the progression of FNH to carcinoma. It is speculated that the associated FNH may represent a hyperplastic response of the adjacent parenchyma to the increased vascularity due to the carcinoma. If a confident diagnosis of FNH can be made on radiologic grounds, conservative management without resection can be considered. Pathologic diagnosis should be sought in all doubtful cases.

Clinical Features.

Large regenerative nodules occur in the setting of cirrhosis, with few exceptions when they are noted in the setting of chronic liver disease without fully developed cirrhosis. These nodules are often incidental findings at autopsy or transplantation but can be noted on radiographic studies. Serum AFP is normal or within the same range as in chronic liver disease or cirrhosis. These nodules are typically seen in cirrhosis due to hepatitis B, hepatitis C, alcohol, and hemochromatosis but are uncommon in primary biliary cirrhosis.

Pathologic Features

Microscopic Features.

These nodules histologically resemble cirrhotic nodules. They have an intact reticulin framework similar to that of normal liver, and the cell plates are one to two cells thick. The hepatocytes typically have normal cytology, although focal variation in cell size, especially scattered large cell change similar to that seen in the other cirrhotic nodules, can be present. Mallory-Denk bodies, bile stasis, clear cell cytoplasmic change, iron or copper deposits, a slight decrease in cell size, and focal or diffuse fatty change may be present. Portal tracts are usually present within the nodule, and bile ductular reaction may be prominent ( Fig. 10.13 ); fibrous septa without the complete triad of duct, vein, and artery may also be present.

Immunostaining for vascular markers such as CD34 or CD31 as a marker for sinusoidal capillarization shows peripheral staining at the edges of the nodule similar to the results seen in cirrhotic nodules. The nodules are negative for AFP.

Significance.

These nodules are generally considered benign lesions and are thought to be large regenerative foci without clonal proliferation. Large regenerative nodules have been associated with an increased incidence of HCC. However, these studies defined macroregenerative nodules histologically by the absence of features of high-grade dysplasia or HCC. Because no clonality studies were done to separate macroregenerative nodules and low-grade dysplastic nodules (LGDNs), it is unclear whether the increased risk is associated with polyclonal large regenerative nodules, clonal LGDNs, or both.

Low-Grade Dysplastic Nodule.

The LGDN in the cirrhotic liver is thought to represent a clonal proliferation of hepatocytes, with a uniform cell population, higher cell density, and features that suggest a clonal proliferation such as accumulation of copper or fat, when the background liver does not show significant steatosis. However, on the basis of gross and standard microscopic features and in the absence of clonality studies, LGDN cannot be reliably distinguished from a large regenerative nodule. In our practice, we do not use the term LGDN and designate all such nodules that lack features of high-grade dysplasia as large regenerative nodules.

High-Grade Dysplastic Nodule

Pathologic Features

Gross Pathology.

These nodules essentially have the same gross appearance as large regenerative and low-grade dysplastic nodules, with the exception that some are not well circumscribed or have irregular edges. Most HGDNs are less than 1.5 cm in largest diameter.

Microscopic Features.

Dysplastic changes may be present uniformly in the nodule or noted as one or more dysplastic foci within a nodule ( Fig. 10.15 ). The atypical features are not overtly diagnostic for HCC. The nodule is often recognized by zones of small cell change with an increased nuclear to cytoplasmic ratio. Increased nuclear density (number of hepatocyte nuclei per microscopic field) is seen compared with the normal liver ( Fig. 10.16 ). Large cell change is rarely a feature of HGDNs, but, if present, the focus must be a discrete zone of atypical cells rather than enlarged nuclei scattered singly in the nodule. Other common features are focal zones of cell plates up to three cells thick, focal decrease in the reticulin framework, and mild dilatation of sinusoids. These nodules can show acinar (pseudoglandular) architecture, Mallory-Denk bodies, fat, clear cell change, cytoplasmic basophilia, bile, and portal tracts. High-grade dysplastic lesions tend to lack iron deposits, in contrast to the regenerative nodules, in which iron deposits are more common.

Dysplasia: Genetic Changes and Outcome.

Progressive genetic changes have been demonstrated in large regenerative nodules, dysplastic nodules, and HCC, supporting the multistep progression of carcinogenesis. Allelic imbalance has been documented in 16% of macroregenerative nodules and 50% of LGDNs. High fractional allelic losses are seen in HGDNs similar to HCC. Losses of 4q, 8p, and Xq are observed in large regenerative nodules and LGDNs, whereas losses of 1p, 13q, 16q, and 17p are seen in high-grade dysplasia. For current clinical management, large regenerative nodules and LGDNs can be followed by imaging and serologic markers, whereas HGDNs are treated more aggressively by surgery or ablative therapy.

Immunohistochemistry.

A variety of novel markers, such as heat shock protein 70 and cyclase-associated protein 2, and gene expression studies have been shown to distinguish HGDN and HCC. These are not part of routine practice yet and need confirmation in larger studies. In recent studies, the combined use of HSP70, GPC3, and GS has been advocated for the distinction between HGDN and eHCC. HSP70 is a potent antiapoptotic, and its overexpression allows cell survival. In a gene expression study comparing early HCC with other hepatocellular nodules, HSP70 was the most abundantly upregulated gene in early HCC ( Fig. 10.20 ). GPC3, an oncofetal antigen, is expressed in 60% to 70% of HCC but not in benign hepatocellular nodules. The expression of GPC3 in HGDN is highly variable across studies ranging from 7% to 22% in most series. GS is one of the genes that is upregulated as a result of nuclear translocation of β-catenin, leading to strong and diffuse cytoplasmic GS staining. Upregulation of GS messenger RNA (mRNA), protein, and activity has been described in human HCC with a stepwise increase from precancerous to early and advanced HCC. In contrast to diffuse expression (>50% tumor cells) in HCC, GS expression in HGDN is typically focal with involvement of less than 50% of tumor cells. The specificity and sensitivity for the diagnosis of HCC when these three markers are used in combination have been cited as 100% and 57%, respectively, when two of the three markers are positive. All three stains are negative in more than 70% of HGDN compared with 3% of early HCC in resection specimens, and all three are positive in 43% of early HCC compared with none of the HGDN.

Clinical Features.

HCC is the most common primary malignant tumor in the liver. It is the fifth most common malignant tumor in men and the eighth most common in women worldwide. More than 500,000 cases are reported every year. The incidence varies with geographic area, being 2 to 7 per 100,000 in Europe and North America and more than 30 per 100,000 in Taiwan, Southeast China, and sub-Saharan Africa. The incidence of HCC more than doubled in the United States in the late 20th century but has since slowed. Men are affected three times more often than women.

Most patients are asymptomatic or have abdominal pain; weight loss, malaise, fever, jaundice, and ascites are seen in fewer than 10% of patients at presentation. Increasingly, patients with cirrhosis are being diagnosed by radiologic techniques or elevated AFP detected on screening. A high serum AFP level (>1000 ng/mL) is seen in almost two-thirds of the cases of large tumors; tumors less than 2 to 3 cm in size are unlikely to have an elevated serum AFP. Elevations of serum AFP up to 500 ng/mL can be seen in many liver disorders, and levels between 500 and 1000 ng/mL are suspicious for HCC but not reliably specific. AFP is also useful for monitoring response to therapy and detection of recurrences. AFP has three glycoforms, and the AFP-L3 fraction may have higher sensitivity in detecting HCC, being present in 45% of tumors less than 2 cm and greater than 90% of tumors greater than 5 cm. Other serum markers that may increase the sensitivity of HCC diagnosis when used with AFP include descarboxyprothrombin (also known as protein induced by vitamin K absence or antagonist [PIVKAII]), GPC3, α- l -fucosidase, and squamous cell carcinoma antigen.

Imaging techniques play a valuable role in diagnosis. Small tumors are hypoechoic on ultrasound, but larger tumors can be hyperechoic. Because HCC receives its principal blood supply from arterial rather than portal blood, it enhances early in the arterial phase with draining of the contrast during the venous phase (venous washout), when the remaining liver shows enhancement. As per the American Association for the Study of Liver Diseases guidelines, typical radiologic features on four-phase CT scan or MRI (unenhanced, arterial, venous, delayed phases) in a tumor greater than 1 cm in cirrhotic liver establish the diagnosis of HCC, and a biopsy is not required for confirmation. However, the real-world efficacy of these guidelines has been questioned and diagnostic pitfalls in radiologic diagnosis of histologic subtypes such as scirrhous HCC have not been adequately studied. Ultrasound follow-up after 3 to 4 months is recommended for lesions less than 1 cm because biopsies from these lesions are challenging to perform and interpret. Biopsy confirmation has been recommended for lesions between 1 and 2 cm and is necessary for all nodular lesions with conflicting radiologic features as well as nodular lesions in noncirrhotic liver. A standardized system for reporting radiology findings in these cases has been devised and is referred to as Liver Imaging Reporting and Data System (LI-RADS). This scheme recognizes five categories based on arterial enhancement, tumor size, venous washout, presence of capsule, and growth compared to prior imaging: LR-1 (definitely benign), LR-2 (probably benign), LR-3 (moderate probability of benign or malignant), LR-4 (probably malignant), LR-5 (definitely malignant). Angiography was formerly used to detect HCC by demonstrating its high vascularity but has been largely replaced by CT and MRI.

A vast majority (>80%) of HCCs develop in cirrhotic livers; the following diseases increase the risk for HCC by causing cirrhosis :

• 1.

  Hepatitis B virus (HBV): This is the most common underlying cause of HCC worldwide, particularly in areas with a high incidence of HCC. The lifetime risk of development of HCC is 50% in HBV-positive men and 20% in women. HCC in this setting occurs at a young age, often in the third decade. Occasional cases can develop in chronic carriers without cirrhosis.

• 2.

  Hepatitis C virus (HCV): This is the principal mechanism underlying HCC in Europe and North America. The risk of HCC in HCV-positive patients is 17-fold compared with negative controls. Nearly all the tumors arise in cirrhosis. Risk factors for development of HCC include older age at HCV acquisition, male sex, obesity, diabetes, heavy alcohol intake, coexistent HBV or human immunodeficiency virus (HIV), and long duration of HCV infection.

• 3.

  Alcohol: Prolonged intake of alcohol (>50 g/day) can lead to cirrhosis and hence is a risk factor for HCC. The risk is higher with coexistent HBV, HCV, and diabetes.

• 4.

  Metabolic disorders: HCC is very common (lifetime risk of 45% in some series) in inherited hemochromatosis. In hereditary tyrosinemia HCC develops in more than one-third of patients who survive until 2 years of age. HCC has also been reported with other metabolic disorders such as α ₁ -antitrypsin deficiency and Wilson disease. Although hepatocellular adenomas are common in type I glycogen storage disease, development of HCC is rare. Metabolic syndrome is a risk factor for HCC even in the absence of steatohepatitis or cirrhosis.

• 5.

  Drugs and toxins: Exposure to thorium dioxide (Thorotrast), aflatoxin, androgenic steroids, and progestational agents has been associated with HCC. Aflatoxin is a fungal toxin of Aspergillus flavus and can contaminate food products stored in damp conditions. Exposure to aflatoxin is common in areas endemic for HBV.

Pathologic Features

Gross Pathology.

The background liver shows cirrhosis in the majority of cases. Tumors can be classified as massive when a solitary large mass is seen, nodular when multiple discrete nodules are seen, and diffuse when multiple small indistinct nodules are seen. Tumors less than 2 cm in diameter are referred to as small HCC; these small tumors usually lack gross vascular invasion, necrosis, or hemorrhage. Tumors are generally soft and may be paler than the adjacent liver or bile stained ( Fig. 10.21 ). Irregular borders and satellite nodules can be present. HCC has a tendency for vascular invasion. Portal and hepatic veins can be involved, and the tumor can extend into the inferior vena cava. Bile duct invasion is not common but can occur. Some HCCs show multinodular growth and can mimic cirrhosis ( Fig. 10.22 ).

Microscopic Findings.

Several typical histologic patterns of HCC have been described by the WHO. The most common is the trabecular pattern, also known as the sinusoidal pattern ( Fig. 10.23 ). The tumor mimics the plate architecture of normal liver, but the cell plates are three cells or greater in thickness, compared with plates that are one to two cells thick in normal or regenerative liver. The tumor cell plates are lined by endothelial cells similar to normal liver, but the reticulin framework is often absent, markedly decreased, or distorted. The tumor cells often have features of small cell change. Large cell change can also be noted but is less frequent except in higher grade tumors. Foci of small or large cell change can be admixed. Kupffer cells are typically absent.

The acinar, pseudoglandular, or adenoid pattern of HCC is less common than the trabecular type. The defining feature in this variant is glandlike spaces, or acini, lined by the hepatocytic tumor cells ( Fig. 10.24 ). The acinar structures are formed by the dilatation or expansion of bile canaliculi and often contain bile. Less frequently, the spaces are a result of central necrosis and may contain protein, cellular debris, or macrophages, but not blue mucin. Because of the formation of glandlike spaces, this pattern can be mistaken for adenocarcinoma. The acinar pattern is frequently admixed with the trabecular pattern ( Fig. 10.25 ).

The solid or compact pattern of HCC is characterized by dense aggregates of tumor cells that seem to lack the endothelial cell–lined trabeculae or cell plates ( Fig. 10.26 ); however, careful examination with endothelial cell markers will often reveal the presence of compressed trabeculae. Loss of the reticulin framework is typically seen in the solid, crowded zones.

The cytologic features of HCC within any of these patterns show great variation. The tumor cells often maintain a polygonal shape and have round vesicular nuclei and prominent nucleoli. Intranuclear vacuoles (representing cytoplasmic invaginations) and glycogenation of nuclei are common findings. Small cell change (as described earlier) is the most common cytologic change, but large cell change and giant and/or pleomorphic cells may be present as a diffuse or focal finding ( Fig. 10.27 ). The amount of cytoplasm may vary, and the cytoplasm is often slightly basophilic compared with normal hepatocytes. The cytoplasm may also have a granular or oxyphilic appearance due to the presence of large numbers of mitochondria ( Fig. 10.28 ). Cytoplasmic inclusions such as Mallory-Denk bodies ( Fig. 10.29 ) or globular eosinophilic bodies ( Fig. 10.30 ), composed of proteins (including albumin, fibrinogen, α ₁ -antitrypsin, or ferritin) may be present. Fat, glycogen, or even water can be prominent, giving the cells a “clear cell” appearance, which has been described as the clear cell variant of HCC ( Fig. 10.31 ). If the entire tumor shows this type of clear cell change and occurs in a noncirrhotic liver, it may be difficult to differentiate from metastatic clear cell tumors such as renal cell carcinoma (RCC). Steatosis can be present and is most pronounced in small tumors less than 2 cm ( Fig. 10.32 ). The fat content tends to decrease as the tumor size increases. Pale bodies are round to oval, lightly eosinophilic, or clear cytoplasmic structures that contain fibrinogen. They are most frequently seen in the fibrolamellar variant (see later discussion) but can be seen in conventional HCC, especially the scirrhous variant. Other less frequent cytoplasmic changes include ground-glass cells containing hepatitis B surface antigen (HBsAg) that are present in some patients with HBV infections and may represent entrapped HBsAg hepatocytes rather than tumor cells. Dark brown to black pigment similar to that seen in Dubin-Johnson syndrome can be present. Iron is typically not seen in the tumor cells but can be present in stromal mesenchymal cells. Rare forms of HCC include a small cell type and sarcomatoid HCC with a prominent spindle cell component. The latter may be difficult to distinguish from a sarcoma, although transitional areas with typical HCC are often present.

The grading of HCC is based on the system developed by Edmondson and Steiner in 1954. The WHO 2010 classification recognizes four categories :

• 1.

  Well-differentiated tumors show a pseudoacinar or thin trabecular pattern and mild nuclear atypia. Most of the tumors are less than 3 cm, and fatty change is often present.

• 2.

  Moderately differentiated tumors have more cytologic and architectural variability with wider trabeculae and more pronounced cytologic atypia. Multinucleated and giant tumor cells can be seen focally.

• 3.

  Poorly differentiated tumors often show a solid growth pattern accompanied by moderate to marked nuclear pleomorphism.

• 4.

  Undifferentiated tumors also show a solid growth pattern with no apparent hepatocellular differentiation and may include sarcomatoid components.

Special histologic types of liver carcinoma recognized by WHO include fibrolamellar carcinoma (see later), scirrhous HCC, undifferentiated carcinoma, lymphoepithelioma-like carcinoma, and sarcomatoid HCC. The scirrhous pattern contains a prominent fibrous stroma ( Fig. 10.33 ) and can be confused with cholangiocarcinoma or fibrolamellar carcinoma. Similar fibrotic changes can occur after radiation or chemotherapy and should not be labeled as scirrhous HCC. Hepatocellular markers such as Hep Par 1 are often negative, whereas adenocarcinoma markers such as CK19, MOC31, and CK7 are positive. The marked fibrosis and aberrant immunohistochemical profile can lead to a misdiagnosis of cholangiocarcinoma. Arginase-1 and glypican-3 have high sensitivity for scirrhous HCC (>90%), and their combined use should be considered in this setting. The term sclerosing HCC was used to describe a variant of HCC characterized by hypercalcemia and marked stromal fibrosis. It is thought that it does not represent a distinct entity and that many of these tumors represent intrahepatic cholangiocarcinomas. Undifferentiated carcinoma is used for primary liver tumors that have epithelial differentiation but lack differentiation along other lines. These tumors are rare and tend to behave aggressively. Lymphoepithelioma-like carcinoma is a rare subtype characterized by syncytial growth pattern, nuclear pleomorphism, prominent intratumoral lymphocyte sheets, and Epstein-Barr virus (EBV) positivity in some tumors. HCC with conventional morphology can also be associated with a dense infiltration of lymphocytes and plasma cells, and formation of lymphoid follicles (HCC with lymphoid stroma). Sarcomatoid HCCs show a component of malignant spindle cells that is indistinguishable from a sarcoma. A classic HCC component can usually be identified by extensive sampling. Sarcomatoid change can occur with chemotherapy and transarterial chemoembolization.

Histologic variants that are not part of the WHO 2010 scheme include steatohepatitic and granulocyte-colony stimulating factor (G-CSF)–producing variants. Steatohepatitic HCC is characterized by typical morphologic features of steatohepatitis in tumor cells such as steatosis, ballooning, and Mallory hyaline. The nonneoplastic liver often shows steatohepatitis associated with metabolic risk factors such as obesity and diabetes. G-CSF–producing HCC shows a prominent neutrophilic infiltrate and can be mistaken for an infectious process. This results from G-CSF production by tumor cells.

Other HCCs with distinctive clinicopathologic features include the encapsulated HCC , pedunculated HCC , small HCC , and pelioid HCC . Tumor encapsulation has been described in 3% to 10% of HCC. Encapsulated HCC is usually small and well differentiated and has a better prognosis after resection. In pedunculated HCC, the tumor is connected to the liver by a pedicle and probably arises from an accessory lobe. These tumors grow slowly and have a better prognosis because of their extrahepatic location. Small HCCs are less than 2 cm by definition. These tumors are often multifocal and well differentiated and occur in cirrhotic livers. Histologically they may show features of early HCC or classic HCC. Large vascular spaces can be seen in HCC mimicking peliosis hepatis, referred to as pelioid HCC. Rarely, HCC may consist entirely of small nodules and closely mimic cirrhosis (see Fig. 10.22 ).

Immunohistochemistry.

Arginase-1, a urea cycle enzyme, is the most sensitive and specific marker for hepatocellular differentiation. It maintains high sensitivity across all patterns of differentiation in HCC as well as in histologic variants such as scirrhous HCC. Hep Par 1 is the most widely used marker and has high sensitivity (80%–90%) for HCC ( Fig. 10.34 ). It can be negative in poorly differentiated and scirrhous HCC. It is usually negative in tumors that commonly enter the differential diagnosis of HCC, including cholangiocarcinoma, most adenocarcinomas from other sites (including pancreas and colorectum), neuroendocrine neoplasms, RCC, adrenocortical carcinoma, malignant melanoma, and angiomyolipoma (AML). However, gastric, esophageal, and lung adenocarcinomas can show strong positive reactions. Polyclonal CEA (pCEA) shows a characteristic canalicular pattern in HCC as it cross-reacts with biliary glycoprotein ( Fig. 10.35 ). HCC is nonreactive with monoclonal CEA. Adenocarcinomas show a cytoplasmic pattern with both polyclonal and monoclonal CEA. The canalicular pattern in HCC can be difficult to interpret; similar patterns have been focally reported in adenocarcinoma. Poorly differentiated HCC may be negative. CD10 staining yields a canalicular pattern similar to polyclonal CEA in HCC. Even though it is rarely positive in adenocarcinoma, its low sensitivity (~50%) does not make it a useful substitute for (or addition to) polyclonal CEA. GPC3 is an oncofetal antigen that is expressed in 70% to 80% of HCCs. It has higher sensitivity than Hep Par 1 for poorly differentiated HCC. Because Hep Par 1 has high sensitivity in well-differentiated HCC, their combined use can complement each other. GPC3 is negative in normal liver and HCAs and hence may be useful in this distinction. HGDNs are negative or focally positive, but overlap with HCC is seen in some instances. GPC3 is also positive in a small minority of melanomas and nonseminomatous germ cell tumors such as a yolk sac tumor and choriocarcinoma. AFP is specific for HCC if a yolk sac tumor can be excluded. However, staining tends to be patchy and often has high background, and sensitivity is low (30%–50%), especially in small, well-differentiated HCC. Albumin in situ hybridization is specific for hepatocellular differentiation and has high sensitivity (>90%). However, this assay is not widely used because of limited availability.

The absence of staining with adenocarcinoma markers can be helpful for the diagnosis of HCC. MOC31, an antibody directed against epithelial cell adhesion molecule (EpCAM), consistently (80%–100%) stains cholangiocarcinoma and adenocarcinoma from a variety of sites such as colorectum, pancreas, stomach, lung, breast, and ovary. It yields a diffuse membranous pattern of staining in adenocarcinoma, which is easy to interpret. Most HCCs are negative for MOC31, but strong expression can be seen in 10% to 20% of cases. CK7, CK19, and CK20 may be helpful in establishing the diagnosis and origin of metastatic adenocarcinoma. CK19 is essentially always positive in cholangiocarcinoma; most HCCs are negative but can be positive in 10% to 20% of cases. CK8 and 18 (CAM5.2 antibody) are often expressed in HCC. CK7 and CK19 expression is more common in poorly differentiated HCC and in variants such as fibrolamellar carcinoma and scirrhous HCC. Other markers can be used for the diagnosis of metastatic adenocarcinoma depending on the clinical situation, such as nuclear thyroid transcription factor 1 (TTF1) for lung, CDX2 for intestinal, GATA3 for breast/urothelial, GCDFP15/mammaglobin/ER/PR for breast, and prostate-specific antigen (PSA)/protein (p501s)/NKX3.1 for prostate. Depending on the clone, nonneoplastic hepatocytes and HCC can show cytoplasmic positivity for TTF1. Estrogen receptor (ER) and progesterone receptor (PR) can be helpful in identifying breast/gynecologic origin but rarely can be positive in HCC.

Differential Diagnosis

• 1.

  Hepatocellular neoplasms. Most of the diagnostic problems arise in distinguishing well-differentiated HCC from HCA or FNH in noncirrhotic liver and regenerative or dysplastic nodules in cirrhotic liver (see respective sections). Reticulin staining can be valuable in the identification of HCC by demonstrating fragmentation and loss of reticulin framework ( Fig. 10.36 ). Occasionally, well-differentiated HCC may have an intact reticulin framework. CD34 typically shows diffuse staining of the endothelial-lined trabeculae in HCC, but a similar pattern can be observed in FNH and HCA. GPC3 can be positive in HCC and is negative in benign lesions; however, its clinical utility is limited by low sensitivity for well-differentiated HCC.

  

• 2.

  Adenocarcinoma (intrahepatic cholangiocarcinoma or metastatic adenocarcinoma) ( Table 10.3 ). The presence of cirrhosis, elevated AFP level, bile production, and trabecular pattern of growth favor HCC. Intrahepatic cholangiocarcinoma is less common, and metastatic adenocarcinoma is rare in cirrhotic liver. The presence of dense fibrotic stroma favors adenocarcinoma but can also be seen in scirrhous HCC. Pseudoacinar pattern is often seen in HCC and hence is not diagnostic of adenocarcinoma. Similarly, multiple lesions are more common in metastases, but HCC can be multifocal. The use of arginase-1 and CK19 can establish the diagnosis in the majority of cases. Additional hepatocellular (GPC3, Hep Par 1, pCEA) markers, adenocarcinoma markers (CK7, MOC31), and site-specific markers can be added depending on the clinical situation. Histochemical stains such as mucicarmine or PAS with diastase can demonstrate mucin in adenocarcinoma. Mucin is absent in HCC, except in combined HCC-CC and in some cases of fibrolamellar carcinoma. Cytoplasmic glycoproteins in HCC can be highlighted by PAS diastase (PAS-D) staining, leading to potentially false-positive interpretation.

  TABLE 10.3

  Differential Diagnosis of Hepatocellular Carcinoma and Adenocarcinoma (Cholangiocarcinoma or Metastatic Adenocarcinoma).

  	HCC	Adenocarcinoma
  Clinical Features
  Cirrhosis	Often present (>80%)	Usually absent
  Number	Usually single; multiple nodules can be seen	Often multiple
  α-Fetoprotein	Elevated; can be normal in tumors <2 cm	Normal
  Morphology
  Pattern	Often trabecular; pseudoglandular pattern can be present	Glandular; less often solid or papillary
  Fibrosis	Usually not prominent, except in scirrhous or fibrolamellar variants	Often prominent
  Mucin	Absent, except for fibrolamellar variant	Can be present
  Bile	Can be present	Absent
  Immunohistochemistry
  Arginase-1	Most sensitive and specific marker	Negative
  Hep Par 1	Highly sensitive and specific; can be negative in poorly differentiated HCC	Negative or weakly positive. Strong reactions can be seen in gastric, esophageal, and lung adenocarcinomas
  Polyclonal CEA	Canalicular pattern	Cytoplasmic pattern
  Glypican-3	High sensitivity, especially for poorly differentiated	Usually negative; rare adenocarcinomas and melanomas can be positive
  α-Fetoprotein	Specific, but low sensitivity (30%–50%)	Negative
  MOC31	Usually negative	Strong membrane positivity in majority of adenocarcinomas
  Keratins	CAM5.2 positive; usually negative for CK7, CK19, CK20	CK7, CK20 profile depends on site; cholangiocarcinomas strongly express CK7, CK19
  Albumin in situ hybridization	Specific for hepatocellular differentiation; sensitivity >90%	Negative

  CEA, Carcinoembryonic antigen; HCC, hepatocellular carcinoma.

• 3.

  Neuroendocrine tumors (NETs). HCC can be difficult to distinguish from a neuroendocrine neoplasm as both can form acinar or trabecular patterns and can be composed of tumor cells with abundant eosinophilic cytoplasm and round nuclei. Features that favor a NET are prominent vascular or capillary network and/or stromal hyalinization. NETs are almost always metastatic but can rarely arise as a primary lesion in the liver. Focal neuroendocrine differentiation has been noted in HCC, including the fibrolamellar variant, as well as in hepatoblastoma, with use of various markers such as neuron-specific enolase, protein gene product 9.5, vasoactive intestinal peptide, calcitonin, and S100. However, diffuse staining with chromogranin or synaptophysin strongly supports a NET.

• 4.

  RCC. Clear cell HCC can pose a diagnostic challenge when it occurs in noncirrhotic liver without significant AFP elevation. The chief differential diagnosis is metastatic clear cell RCC. Hepatocellular markers such as arginase-1 and Hep Par 1 are positive in clear cell HCC but are negative in RCC, whereas PAX2, PAX8, RCC marker, epithelial membrane antigen (EMA), vimentin, and MOC31 are expressed in clear cell RCC but are negative in HCC. PAX2, a renal-tubular nuclear transcription factor, has high sensitivity, being expressed in 70% to 80% of metastatic clear cell RCCs and less commonly in other subtypes of RCC. Addition of the RCC marker can increase the sensitivity. Keratin profiles are not helpful as both are positive for CAM5.2 and generally negative for CK7 and CK20. CD10 shows membranous staining in RCC compared with canalicular pattern of staining in HCC, but it may be difficult to distinguish these patterns in the setting of a biopsy.

• 5.

  Adrenocortical carcinoma. These tumors can have overlapping histologic features with clear cell HCC. The expression of inhibin, Melan A, and calretinin in adrenocortical carcinoma distinguishes it from HCC. Inhibin is expressed in around 70% of adrenocortical carcinomas and Melan A in 50% to 60%. The sensitivity can be improved to greater than 80% by combination of both antibodies. Adrenocortical carcinomas express synaptophysin but are negative for chromogranin. Most adrenocortical carcinomas are negative for keratin and for hepatocyte markers such as arginase-1 and Hep Par 1.

• 6.

  Melanomas. These tumors can histologically mimic HCC, but positivity for S100 and melanocytic markers (Sox10, HMB45, Melan A, tyrosinase, microphthalmia-associated transcription factor) and absence of hepatocellular markers such as arginase-1 and Hep Par 1 easily establishes the diagnosis. GPC3 can be positive in melanoma.

• 7.

  Angiomyolipoma. The epithelioid variant of AML can be difficult to distinguish from well-differentiated HCC. Most AMLs in the liver are not associated with tuberous sclerosis and often lack a fatty component. The presence of bile or Mallory-Denk bodies can help in this distinction, as these features are not seen in AML. Once the diagnosis is suspected, immunohistochemical confirmation is easy because of their characteristic staining profile. AMLs strongly coexpress smooth muscle markers, such as smooth muscle actin (SMA) or desmin, and melanocytic markers such as HMB45, Melan A, tyrosinase, and microphthalmia-associated factor. Focal S100 expression can be seen in AML, generally in the epithelioid and fat cells. Keratin, arginase-1, and Hep Par 1 are negative (see later discussion).

Molecular Genetic Features.

Low-grade necroinflammatory activity associated with chronic liver disease and cirrhosis produces cytokines and other cytotoxic moieties, such as nitric oxide and free oxygen radicals, which lead to DNA damage. The repeated cycles of necrosis and regeneration render the cells susceptible to mutations, and time may be insufficient to repair DNA damage due to rapid cell turnover. The preneoplastic phase is characterized by overexpression of transforming growth factor-α and insulin-like growth factor-2, which lead to accelerated hepatocyte proliferation.

Comparative genomic hybridization has revealed a fairly consistent pattern of chromosomal gains and losses in HCC. The most prominent changes are gains of part or entire chromosome arms 8q (49%–81%), 1q (60%–79%), and 7q (40%–64%), and loss of 16q (36%–65%). Other common abnormalities include overrepresentation at sites Xq and 5p and losses at 4q, 8p, 13q, 16q, and 17p. Certain clinicopathologic associations have been noted with specific abnormalities. Gain of 8q and loss of 13q are seen more often in HCC arising in noncirrhotic liver. Chromosome 9p and 6q losses have been reported to be independent predictors of poor outcome. Mutations of the p53 gene are common in HCC and are reported in 30% to 50% of cases in most studies. The prevalence varies widely between geographic areas, with low or none in Australia to 67% in Senegal. Dietary exposure to aflatoxin is associated with a specific G→T transversion at codon 249 of the p53 gene. In hepatitis B, the HBx protein encoded by the X region of HBV has been linked to functional inactivation of the p53 protein. Viral proteins encoded by the HCV genome, such as NS3 and NS5A proteins, also interfere with p53 activity. The mutation rate may be as high as 40% in HCC associated with hepatitis C. It has been suggested that two main pathways of hepatocarcinogenesis exist: one demonstrating β-catenin mutations and limited genetic alterations such as 8p loss and the other with widespread allelic losses at multiple chromosomal sites, p53 mutations, and no β-catenin mutations. The latter tumors are often poorly differentiated and behave more aggressively. Mutations in β-catenin, a critical component of the Wnt signaling pathway, are seen in 20% to 30% of HCCs. Abnormalities in cell cycle regulation are common in HCC. Inactivation of p16 by hypermethylation of the promoter region or loss of retinoblastoma protein Rb through gene mutation occurs in around 40% of HCC. Reduced expression of inhibitors of cyclin-dependent kinases, p21 and p27, has been reported in 38% and 52% of HCC, respectively. The core protein produced by HCV can also lead to repression of the p21 promoter. Activation of the Akt-mTOR pathway is frequent in HCC and may play a role in angiogenesis.

Many molecular changes have been identified as potential prognostic markers. Tumors with inactivation of p53 , Rb , and p16 genes and allelic losses of 9p, 6q, and 14q have been reported to be associated with adverse outcome. Immunohistochemical expression of p53 in tumor cells is associated with worse prognosis. β-catenin mutations and high expression of p27 correlate with better survival, whereas overexpression of cyclin D is a marker for early relapse. High proliferative rate, low E-cadherin expression, and nuclear β-catenin expression are predictive of recurrence after transplantation. However, none of these findings has been shown to be specific enough in large series to be used clinically. Mutations in the telomerase reverse transcriptase (TERT) promoter region are seen in around 60% of HCC and 25% of cirrhotic nodules. In the last few years, aberrant expression of microRNA has been implicated in HCC. MicroRNA signatures have been described for the diagnosis and prognosis of HCC. Upregulation of certain microRNAs such as mir-221 and mir-21 is associated with aggressive behavior.

Several HCC classifications have been proposed based on gene expression signatures. In one scheme, three subclasses of HCC are recognized: S1 (activation in Wnt signaling pathway), S2 (high proliferation, activation of MYC and AKT , elevated AFP, positive MOC31), and S3 (well differentiated, expression of hepatocyte function–related genes). These subtypes correlate with clinicopathologic parameters such as higher vascular invasion and recurrence in S1 tumors. Transcriptome analysis has identified six subgroups of HCC : G1 (overexpression of fetal genes, AKT pathway), G2 (high HBV copy number, PIK3CA and TP53 mutations, AKT pathway), G3 ( TP53 mutation, overexpression of cell cycle genes), G4 ( TCF1 mutation), G5 and G6 (Wnt pathway activation often due to β-catenin mutations).

Treatment and Prognosis.

For patients without cirrhosis and with no evidence of vascular invasion or extrahepatic disease, resection is the treatment of choice. Survival in patients without cirrhosis has been reported to be 40% and 26% at 5 and 10 years, respectively. Survival is worse in patients with cirrhosis, but 5-year survival of 33% to 44% can be achieved with tumors less than 5 cm, no vascular or extrahepatic involvement, and good functional status (Child-Pugh class A). Liver transplantation is the best treatment for HCC in patients with cirrhosis. Transplantation is contraindicated with tumors greater than 5 cm, more than three tumors, multiple tumors with one of them greater than 3 cm, and extrahepatic spread. When these criteria are followed, 5-year survival greater than 75% has been achieved. It has been suggested that the size of eligible solitary tumors should be increased to 6.5 cm. Treatment of HCC using ethanol or radiofrequency ablation can be done under ultrasound or CT guidance. Ablative techniques are often used for small tumors that are considered unresectable because of their location or coexistent advanced liver disease, as well as in patients awaiting transplantation.

The overall prognosis in HCC remains poor, with 5-year survival at 10%. Poor survival is associated with male sex, advanced age, AFP greater than 100 ng/mL, poor differentiation, cirrhosis, keratin 19 expression, and p53 mutations. Tumors with encapsulation, small size, and a prominent intratumoral inflammatory infiltrate are associated with better outcome. The histologic pattern is considered less significant prognostically, although a trabecular pattern has been reported to correlate with aggressive behavior, whereas the pelioid pattern may have a better outcome. Vascular invasion, lymph node metastases, and a positive surgical margin correlate with recurrence after resection. Radiotherapy and chemotherapy are usually not effective in HCC. Sorafenib, a tyrosine kinase inhibitor, can marginally increase survival and slow disease progression in advanced HCC, and other tyrosine kinase inhibitors have also shown limited benefit.

Clinical Features.

Fibrolamellar carcinoma (FLM) occurs in the noncirrhotic liver in young adults (mean age 26 years, women > men). Clinical presentation may include abdominal pain or swelling, anorexia, weight loss, jaundice, and, rarely, hemoperitoneum. No definitive risk factors have been identified. FNH-like nodules have occasionally been seen at the periphery of FLM and may be the result of local perfusion abnormalities rather than a benign precursor of FLM. Serum AFP levels are usually normal; rare tumors with high levels have been reported. The central scar can be demonstrated by CT or MRI and does not show enhancement, unlike the scar in FNH.

Pathologic Features

Gross Features.

FLM is a firm, tan-white to brown, well-circumscribed but unencapsulated, lobulated mass that arises in a background of normal liver ( Fig. 10.37 ). Most tumors are large and can measure up to 17 cm. The larger tumors can show foci of hemorrhage and necrosis. Although 60% to 70% of tumors are single, multiple tumors, generally in the form of satellite lesions, may be present. Unusually frequent involvement of the left lobe has been noted. A prominent central stellate scar similar to that of FNH can be present and can also be seen in lymph node metastases.

Microscopic Features.

The hallmark features of FLM are large polygonal tumor cells with abundant eosinophilic granular cytoplasm, prominent macronucleoli, and lamellar bands of fibrosis ( Fig. 10.38 ). The collagen lamellae consist of platelike stacks of connective tissue of variable thickness. The lamellar pattern is not uniformly seen throughout the tumor but is often present in half of the tumor in most cases. The tumor cells are typically arranged in cords or nests. In addition to prominent nucleoli, the nuclei show intranuclear cytoplasmic invaginations and margination of chromatin. The cytoplasmic granularity is due to the presence of abundant mitochondria. Other cytoplasmic features include “pale bodies,” which may contain fibrinogen and/or albumin. PAS-D–positive material, probably representing glycoprotein secretions, can be present. Bile plugs are common, but fat is usually absent. Other features that can occasionally be present are acinar structures, mucin secretion, multinucleated tumor cells, copper, epithelioid granulomas, and peliosis hepatis. Tumors with areas resembling classic HCC and FLM have been described ; it is not clear whether this represents a variant of FLM or a mixed FLM–conventional HCC. These tumors tend to occur at older age or in patients with viral hepatitis and are likely to be more closely related to classic HCC.

Immunohistochemically, FLM resembles classic HCC and expresses Hep Par 1, polyclonal CEA, and GPC3. AFP immunoreactivity is uniformly absent. Neuroendocrine markers (see earlier discussion) have been reported to be focally positive but have no known clinical significance. CK7 is expressed in nearly all FLM compared with 10% to 30% of classic HCC. The combination of CK7 and CD68 has been advocated for FLM, as both are positive in nearly all cases. The diagnosis of FLM should be made with caution if either of these stains is negative. However, these stains are not specific and can be positive in classic HCC. Several genetic abnormalities seen in classic HCC, including p53 mutations, β-catenin mutations, and a high level of chromosomal instability, are not seen in FLM. Recently, deletion of about 400 kilobases on chromosome 19 has been described in FLM. This leads to a novel DNAJB1-PRKACA fusion transcript due to in-frame fusion of the promoter and first exon of DNAJB1, a heat shock protein, and nine trailing exons of PRKACA, the catalytic domain of protein kinase A. This can be identified by reverse transcription polymerase chain reaction (RT-PCR) as well as fluorescence in situ hybridization (FISH). This deletion has been reported in more than 80% of FLMs, but not in classic HCC, hepatoblastoma, or intrahepatic cholangiocarcinoma, and is diagnostically useful.

Treatment and Prognosis.

FLM is an aggressive tumor with 5-year survival of less than 50%. Complete excision of the involved lobe is the current therapy of choice. When the tumor location or extent precludes resection, liver transplantation can be performed, but the outcome is less favorable. Several studies have shown that FLM has a better prognosis than classic HCC. However, outcome in FLM and classic HCC arising in noncirrhotic liver is similar. The apparently better outcome in FLM may be related to lack of cirrhosis and higher resectability rate rather than due to its unique clinicopathologic features.

Clinical Features.

This is a rare tumor that represents fewer than 5% of primary liver tumors. It is more closely related to HCC, as evidenced by its frequent association with HBV or HCV infection and cirrhosis.

Pathologic Features.

The diagnosis is based on the demonstration of both hepatocellular and glandular differentiation ( Fig. 10.39 ). According to WHO criteria, the hepatocellular component is identified by a trabecular growth pattern, bile production, or intercellular bile canaliculi. The cholangiocellular component is identified by definite gland formation or mucin production. The diagnosis can be confirmed immunohistochemically by demonstrating the HCC component with arginase-1, Hep Par 1, and/or GPC3, and the cholangiocarcinoma component by MOC31, CK7, and/or CK19. Areas of transition between HCC and cholangiocarcinoma are often present. The transitional areas show morphology intermediate between HCC and cholangiocarcinoma and can have cells with morphology and immunophenotypic characteristics of stem cells. If these cells predominate, the designation of combined cHCC-CCA with stem cell features was proposed by WHO in 2010 and three morphologic subtypes were described: typical, intermediate, and cholangiolocellular. However, none of the putative stem cell markers such as KIT, CD56, and CK19 are specific for stem cells, which makes it challenging to reliably make this diagnosis. Hence cHCC-CCA with stem cell features as well as its three subtypes are not well-established entities. The cholangiolocellular subtype appears to recapitulate canals of Hering and is more likely to be a variant of cholangiocarcinoma. The diagnosis of combined cHCC-CCA should not be made when HCC component is accompanied by stem cell features, but only when both HCC and CC components are present.

The histogenesis of combined HCC-CC remains uncertain. It may be a collision of HCC and cholangiocarcinoma or may represent a single tumor with divergent differentiation. In the former case, the tumor would presumably be biclonal with no intimate admixture of HCC and cholangiocarcinoma components. The latter would presumably arise from a single clone with HCC or cholangiocarcinoma arising first and then transforming to the other, or origin from intermediate cells with divergent differentiation. Genetic studies have shown that the majority of combined cHCC-CCAs arise from the same clone and share abnormalities with conventional HCC such as allelic losses of 4q, 8p, 17p, and 13q.

Prognosis and Therapy.

The prognosis is poor, and the disease is more aggressive than conventional HCC. After resection, the 5-year survival is 24%. In unresectable cases, almost all patients die within 2 years. The outcome in combined cHCC-CCA with stem cell features is unclear because of the small number of cases studied and lack of uniform diagnostic criteria.

Clinical Features.

HB is the most common malignant liver tumor in children and comprises approximately 1% of pediatric cancers. Nearly 90% of cases occur between the ages of 6 months and 5 years. This tumor can occasionally arise in older children and, very rarely, in adults. The lesion has a male preponderance of almost 2 : 1, but the sex incidence is similar in older patients. Associations with other congenital conditions such as Beckwith-Wiedemann syndrome, cleft palate, diaphragmatic hernia, Down syndrome, familial polyposis coli, hemihypertrophy, renal malformations, and other chromosomal abnormalities are noted in one-third of cases. Most patients present with an asymptomatic abdominal mass. Weight loss, anorexia, and a rapidly enlarging abdominal mass are common presenting symptoms. Less-common symptoms include vomiting, diarrhea, and jaundice. Rarely, signs of precocious puberty such as virilization may be the presenting feature, which is associated with production of human chorionic gonadotropin by the tumor. Serum AFP is nearly always elevated and has proved to be a useful marker for tumor recurrence or metastasis after therapy. Zonal liver involvement, vascular invasion, and extrahepatic extension are determined by imaging to determine the PRETEXT ( pret reatment assessment of disease ext ent) stage and evaluate resectability.

Pathologic Features

Gross Pathology.

HB occurs in the noncirrhotic liver, typically as a large, single mass. The gross appearance can be variable, but the tumor is often multinodular with foci of hemorrhage and necrosis ( Fig. 10.40 ). Because different nodules or zones within the tumor can represent different histologic components, which in turn may correlate with prognosis, adequate sampling of multiple areas must be undertaken. After chemotherapy, tumors may be very necrotic, and the mesenchymal components, especially osteoid, often appear prominent ( Fig. 10.41 ).

Microscopic Features.

The two morphologic subtypes of HB are the epithelial (55%) and the mixed epithelial-mesenchymal (45%). The epithelial type may show an embryonal pattern, fetal pattern ( Fig. 10.42 ), or a mixture of the two ( Fig. 10.43 ). The mixed epithelial-mesenchymal subtype is composed of admixed epithelial and mesenchymal components with or without teratoid elements.

The embryonal pattern is the more “immature” form and consists of small tumor cells arranged in cords, ribbons, rosettelike structures, or tubules. The cells have round, oval, or elongated nuclei, prominent nucleoli, and scant cytoplasm; mitoses are rare. The fetal pattern is the more “mature” form that closely resembles fetal liver with tumor cells arranged in plates or cords. The tumor cells in the fetal pattern are typically smaller than normal hepatocytes but are slightly larger than the tumor cells in the embryonal pattern and have moderate amounts of eosinophilic and/or clear cytoplasm. The clear cell change is due to the presence of lipid and/or glycogen. Both eosinophilic and clear cytoplasmic features often occur in the same tumor and result in a distinctive alternating pink and white appearance. The nuclei in the fetal pattern are typically small and round, similar to normal fetal liver cells. A subset of fetal HBs shows higher mitotic activity (≤2 per high-power field [hpf]) and larger, more pleomorphic closely packed nuclei, referred to as the crowded fetal pattern. Tumors that are entirely composed of the fetal pattern without crowded fetal features are termed pure fetal HB . For both embryonal and fetal patterns, extramedullary hematopoiesis is often present. Mixed embryonal and fetal patterns are common.

Less-common epithelial subtypes of HB include the small cell undifferentiated type and macrotrabecular type, which together account for around 5% of cases. The small cell type consists of sheets of tumor cells with scant cytoplasm similar to other small blue cell tumors such as neuroblastoma, Ewing sarcoma, lymphoma, and embryonal rhabdomyosarcoma. No evidence of hepatocellular differentiation is present. The identification of other typical patterns of HB helps in establishing the diagnosis. The macrotrabecular type forms wide trabeculae greater than 10 cells thick. The trabeculae may comprise large cells with moderate cytoplasm mimicking HCC (MT1 pattern) or fetal and/or embryonal-type tumor cells (MT2). The presence of other patterns of HB and the occurrence in noncirrhotic liver can help to distinguish this variant from HCC. A tumor with a limited macrotrabecular component should be classified according to the other predominant patterns. Ductular differentiation has been described at the periphery of some epithelial subtypes (cholangioblastic HB) and can be confused with ductular reaction at the tumor periphery, especially after chemotherapy.

The epithelial components (embryonal, fetal, or both) are accompanied by a mesenchymal component in nearly half of the cases. In 80% of mixed tumors, the mesenchymal component is represented by immature fibrous tissue, osteoid, and/or cartilage. The remaining 20% are mixed HB with teratoid features and show additional tissue types such as intestinal-type glandular elements, squamous epithelium, mucinous epithelium, melanin pigment, skeletal muscle, or neural tissue.

Differential Diagnosis.

Pure fetal HB can be histologically similar to HCA. The tumor cells tend to be smaller in HB than in HCA, and the alternating pink and white cytoplasmic staining pattern of HB is typically not present in adenoma. Clinical parameters can be very helpful in separating the two lesions as HCA essentially does not occur before age 5 years, except in association with a metabolic disorder such as glycogen storage disease, and serum AFP is not elevated in HCA. The clinical setting also plays an important role in distinguishing the macrotrabecular variant of HB and HCC, as the latter may occur in this young age group in the presence of a preexisting liver disease or metabolic disorder, usually in the setting of cirrhosis. GPC3, diffuse glutamine synthetase, and nuclear β-catenin is seen more often in HB than in HCC. The presence of other patterns of HB is helpful in the diagnosis of uncommon patterns such as small cell undifferentiated and macrotrabecular variants. HB with predominant embryonal or small cell undifferentiated patterns can mimic other small round cell tumors such as Wilms tumor, Ewing sarcoma or primitive neuroectodermal tumor (PNET), and neuroblastoma. Diffuse GPC3 expression (embryonal HB) and nuclear β-catenin (both embryonal and small cell undifferentiated) help in establishing the diagnosis of HB. Mixed HB with teratoid features should be distinguished from teratomas. The latter lack the fetal and embryonal epithelial components of HB. Calcifying nested epithelial stromal tumor can be confused with HB (see later).

Molecular Genetic Changes.

HB cells are usually diploid or hyperdiploid and show limited cytogenetic alterations, often involving chromosomes 1, 2, 8, and 20. The most frequent alterations are trisomies of chromosomes 2 and 20. Rearrangements involving chromosomes 1q and 2q and gains of chromosome X have also been reported. Loss of heterozygosity (LOH) of maternal 11p15 is seen in one-third of HBs. This is characteristic of patients with Beckwith-Wiedemann syndrome who have an increased risk of development of HB. Imprinted genes on 11p15 such as IGF2 may play an important role in HB. Gene expression studies show activation of the Wnt/β-catenin signaling pathway in all subtypes with higher activation in more aggressive subtypes. Nuclear localization of β-catenin can be demonstrated in the majority of HB by immunohistochemistry. It occurs more frequently in embryonal and undifferentiated HB compared with fetal type and is associated with poor survival in some studies but not in others. APC mutations occur in sporadic HB, as well as cases associated with familial adenomatous polyposis. Abnormal cell cycle regulation by inactivation of the p16 gene by hypermethylation has been implicated in the pathogenesis. Compared to fetal liver, HBs show upregulation of antiapoptotic genes and downregulation of proapoptotic genes.

Prognosis and Therapy.

Prognosis is directly related to complete surgical excision and tumor stage. The 5-year survival is around 75%. The treatment of choice is complete surgical resection, but chemotherapy is often used before surgery to reduce tumor size, as well as for residual and unresectable tumors. Liver transplantation is a treatment option for children with multifocal, bilobar, or recurrent HB without extrahepatic extension. The stage of the tumor is the single most important prognostic factor. The Children's Oncology Group staging system for HB is shown in Table 10.4 . Some histologic subtypes, such as pure fetal, have a better outcome after complete resection. Pure fetal subtype may be cured with surgical resection alone, while surgical resection along with cisplatin/doxorubicin-based chemotherapy is indicated in other histologic subtypes. Small cell and macrotrabecular subtypes are associated with poor prognosis. Tumor-free margins are important, but vascular invasion does not have a significant impact on survival. Other factors associated with an adverse outcome are age of presentation under 1 year, large tumor size, and involvement of vital structures.