Tumors of the liver: Pathologic aspects

Clinical and epidemiologic background

Hepatocellular carcinoma (HCC) accounts for 75% to 85% of primary malignant liver tumors in adults, ranking as the sixth most common cancer and the fourth leading cause of cancer-related death worldwide. ^,

One of the striking characteristics of HCC is the marked geographic variation in its frequency, which is mainly related to geographic distribution of chronic liver disease–related risk factors (see Chapters 68 and 74 ). East Asia and sub-Saharan Africa have a very high incidence, whereas Italy, Spain, and Latin American countries are at intermediate risk. A relatively low but increasing incidence is found in Western Europe, the United States, Canada, and Scandinavia. The major known risk factors for HCC are hepatitis viruses (chronic hepatitis B [HBV] and hepatitis C [HCV]), toxic agents (alcohol and aflatoxins), metabolic diseases (metabolic syndrome, α-1 antitrypsin deficiency and Wilson disease), hereditary hemochromatosis, and immune-related diseases (primary biliary cirrhosis and autoimmune hepatitis). Given that the burden of chronic liver diseases is expected to rise, it is expected that the incidence of HCC will also increase in the future, especially with the pandemic obesity and metabolic syndrome. In addition, despite very effective treatment for viral hepatitis, the risk of developing cancer persists in HCV infection after viral eradication and remains significant in hepatitis B (see Chapters 68 and 74 ).

HCC is primarily a disease of older men, and its incidence generally increases with age. In Western Europe and the United States, most patients with HCC are between 50 and 75 years of age. It occurs more frequently in men than women with a male-to-female ratio ranging from 2:1 to 9:1, although the reason is not clear. Serum α-fetoprotein (AFP) is elevated in most symptomatic tumors, but small cancers are associated with lesser or even normal levels. Thus serum AFP is not a reliable diagnostic test for HCC screening patients with cirrhosis.

The association between cirrhosis and HCC is well established. Indeed, 60% to 90% of HCC arises in cirrhotic livers. Conversely, approximately 1% to 3% of patients with cirrhosis will develop HCC annually. It is admitted that HCC usually occurs after a mean delay of 10 years after the constitution of liver cirrhosis. This observation is highly consistent with a multistep process that implies progressive malignant transformation of preneoplastic lesions such as macroregenerative and dysplastic cirrhotic nodules. This progression parallels the growing accumulation of genetic and epigenetic abnormalities into liver cells from regenerative to malignant nodules. Nevertheless, it has been widely recognized that in patients with metabolic syndrome, HCC may develop in absence of advanced liver fibrosis in up to 45% of cases, suggesting the involvement of specific mechanisms probably related to the pathogenesis of the underlying disease rather than fibrosis alone.

Pathologic processes of HCC are peculiar for several aspects. Indeed, its morphologic patterns are varied beyond the classic classification based on growth pattern and tumor differentiation (see Chapter 74 ). Furthermore, molecular pathogenesis of HCC is complex, involving different molecular pathways that may reflect different etiologic factors and various underlying liver disease conditions, and it may help in identification of new therapeutic targets. Accordingly, a pathomolecular classification of HCC describing the main histologic subtypes related to molecular alterations has been proposed.

Gross pathology

HCC can adopt a wide range of gross configurations. Several macroscopic classifications have been proposed, but their clinical relevance has not yet been proven.

Tumor size ranges from less than 1 cm (occult HCC) to over 30 cm in diameter. At time of diagnosis, the mean size of HCC arising on cirrhotic liver is usually inferior to those occurring in nonfibrotic liver. HCC tumors less than 2 cm are recognised as “small” or “early HCC”. Small HCCs have been subdivided into vaguely nodular and well-circumscribed HCC, two patterns with differences in prognosis, with the vaguely nodular form having a better prognosis than the well-circumscribed one. ^, Although the diagnosis of large HCC relies mainly on imaging modalities, biopsy is often requested for the diagnosis of these small nodular lesions.

At gross examination, overt HCC may display a nodular, infiltrative, or diffuse macroscopic pattern. The nodular (expanding) pattern is the most common type. It is typically seen in association with cirrhosis. This group of HCCs is characterized by a sharp demarcation between the tumor mass and the compressed and partly atrophic surrounding parenchyma ( Fig. 87.1 ). The nodule may be single or multiple across the liver when developed as a complication of cirrhosis. When nodules are multiple, small nodules, less than 1 cm in diameter and adjacent to the main tumor nodule (usually within 2 cm), they are considered satellite nodules ( Fig. 87.2 ). In cases of multiple HCCs, nodules may represent either multifocal independent tumors or intrahepatic metastasis. Such distinction is quite impossible based on pathologic study alone but could be addressed with surrogate molecular analysis. ^, On cut section, nodular HCC is circumscribed totally or partly by a fibrous capsule. Capsule formation is considered to begin at a tumor diameter of at least 10 mm or greater because no distinct capsule was noted in lesions less than 10 mm. The prognostic significance of capsule formation has not yet been definitively settled. HCCs typically form soft masses that vary in color from gray, light brown, or yellow-green, depending on their content of fat or bile, often punctuated by foci of hemorrhage or necrosis when the tumor reaches a significant volume ( Fig. 87.3 ).

The infiltrative (massive) pattern is usually characterized by a large single mass that occupies a substantial portion of the liver. The lesion is poorly circumscribed with ill-defined, invasive borders ( Fig. 87.4 ). On cut section, the tumor extends into and distorts the adjacent nontumor tissue, interdigitating with surrounding parenchyma. Vessels are incorporated into and not displaced by the tumor mass so that tortuous vessels around the tumor are not so obvious.

The diffuse (or cirrhotomimetic) pattern is the least common and represents a widespread infiltration by numerous small nodules that virtually replace the entire liver. In this pattern, the tumor consists of several unconnected small tumors of roughly similar size. Multicentric origin or intrahepatic spread after portal vein invasion have been discussed as pathogenic mechanisms ( Fig. 87.5 ).

Pedunculated HCC is noted in rare instances, presumably reflecting an origin from an accessory hepatic lobe. The identification of the pedunculated form of HCC is significant because even in the case of large tumors, limited resection may give excellent results.

This gross classification has limitations because categorization of a tumor within one single growth pattern may be difficult. Expanding HCC may show areas of infiltrative pattern. Finally, along with the diffuse pattern, which is associated with a dismal prognosis, differentiation between expanding and infiltrative patterns does not appear to be a prognostic indicator.

In advanced HCC, invasion of large veins is common even at gross examination (see Chapter 14 ). The portal vein is more often involved than hepatic veins, inferior vena cava, or right atrium ( Fig. 87.6 ). Portal vein invasion may be associated with thrombosis. Vascular invasion should be determined with care at the initial gross examination (macrovascular invasion). In some instances, intravascular tumor plugs in the close periphery of a large tumor may be difficult to distinguish from satellite tumor nodules. Invasion of large bile ducts producing biliary obstruction and hemobilia might be occasionally found.

Histopathology

Histopathologic evaluation is no more systematic before treatment because dynamic imaging has high diagnostic accuracy for tumors larger than 2 cm. When imaging remains inconclusive, ultrasound (US)-guided biopsy is indicated, especially in nodules smaller than 2 cm in diameter, a situation in which biomarkers have low predictive values and hyperarterialization may be incomplete or absent. For nodules smaller than 1 cm, biopsy is generally not recommended because of its limited performance. These diagnostic criteria have been endorsed by most international liver diseases associations. ^, Nevertheless, and despite the major advances in radiologic procedures, the definitive diagnosis continues to be often primarily based on accurate examination and interpretation of histologic material for any small or atypical nodule. Moreover, a more active biopsy strategy is increasingly proposed, aiming to adapt therapeutic strategies.

Histopathologically, the diagnosis of HCC is based on the resemblance between tumor cells and normal hepatocytes. Therefore the microscopic evaluation entails the assessement of cytologic characteristics of tumoral cells and evaluation of their architectural pattern. ^, Tumoral cells may present varying degrees of hepatocellular differentiation within a single tumor. Nuclei are usually basophilic, often irregular with prominent nucleoli and a high nuclear-to-cytoplasmic ratio. In well-differentiated HCC, the tumor cells may closely resemble normal hepatocytes with a polygonal shape, distinct cell membranes, and eosinophilic granular cytoplasm ( Fig. 87.7 ). Bile canaliculi often can be seen by light microscopy or demonstrated by immunostaining. When dilated, they might contain bile pigment, a characteristic feature of hepatocellular differentiation. Accumulation of glycogen or fat in tumor cells may produce a clear cell appearance ( Fig. 87.8 ). Mallory-Denk bodies, hyaline globules, or eosinophilic ground-glass–like cytoplasmic inclusions can be observed.

As the tumor evolves to poorly differentiated phenotype, cell-to-cell heterogeneity, bizarre nuclei, or giant tumoral cells may appear. Mitosis and apoptotic bodies can be observed ( Fig. 87.9 ). Different degrees of cellular differentiation are usually present within a single large tumor, although small HCCs tend to be more homogeneous.

Growth patterns

The arrangement of the cells contributes to the variety of microscopic appearances. On this basis, three main growth patterns that may co-exist within a nodule are described. The main architectural patterns of growth of HCC are as follows:

• 1.

  Trabecular growth, in which tumoral hepatocytes are arranged in plates varying in thickness from 2 to over 20 cells. Macrotrabecular pattern is commonly used for trabecular proliferations being at least 7 cells thick ( Fig. 87.10 ). This feature resumes the normal trabecular arrangement of liver plates. Neoplastic cells are organized along simplified sinusoids lined by flat endothelial cells, with few or no Kupffer cells. Compared with normal liver plates, the reticulin framework is commonly sparse or absent.

  

• 2.

  A compact or solid pattern occurs when the trabeculae are closely aligned, and the sinusoids become compressed and unapparent. It may co-exist with a macrotrabecular pattern and shows a worse prognosis.

• 3.

  The acinar or pseudoglandular pattern results from either gland-like dilatation of the canaliculi between tumor cells (lumens can contain bile) or central degeneration of trabeculae (lumen containing mainly degenerative products with fibrin) ( Fig. 87.11 ). Like the trabecular pattern of growth, stroma is typically sparse. The lack of a desmoplastic stroma reaction is a helpful diagnostic clue when other glandular malignant epithelial neoplasms, especially cholangiocarcinomas, are discussed. On occasion, large vascular lakes resembling peliosis can develop within the pseudoglandular formations.

  

Hepatocellular carcinoma subtypes

HCCs can be further classified into subtypes that represent distinct clinicopathologic entities. High-throughput molecular studies have provided several molecular classifications of HCC, identifying different subclasses, mostly linked to clinical context (including etiologic factors) and prognosis (including tumor recurrence and survival). ^{, ,} Schematically, HCCs are divided into two main groups, one associated with chromosomal stability and showing a better prognosis, and the other associated with chromosomal instability and showing a worse prognosis. Based on the G1 to G6 classification, a pathomolecular classification has been proposed based on pathologic features specifically associated with the molecular patterns (see Chapter 9B ).

Steatohepatitic subtype.

Initially described HCV infection in transplanted patients and then in patients with alcoholic or metabolic clinical context, the steatohepatitic subtype (SH-HCC) is characterized by morphologic hallmarks recapitulating the nonalcoholic steatohepatitis (NASH) picture, including steatosis, ballooning malignant hepatocytes, Mallory-Denk bodies within tumor cells, inflammatory infiltrates, and pericellular fibrosis ( Fig. 87.12 ). To note, there is no consensual definition of SH-HCC, which may be referred to as HCC showing an SH pattern in more than 5% to more than 50% of tumor area according to the series. In addition, the number of elementary features (steatosis, ballooned cells, Mallory-Denk bodies, inflammation, and fibrosis) required for the diagnosis may vary.

Macroscopically, SH-HCC is nodular, well-limited, and more yellowish (because of steatosis) compared with other subtypes ( Fig. 87.13 ). In one study, SH-HCC tended to be smaller and better differentiated independently of the presence of cirrhosis in the background liver. These HCCs were assigned to the G4 transcriptomic subgroup characterized by a lack of Wnt/β-catenin pathway activation and low GS expression. ^, Although no significant changes in the gene involved in lipid metabolism were observed, activation of the interleukin-6 (IL-6)/AKT/STAT pathway was frequent in this subgroup, which is consistent with the involvement of this pathway in the transition from nonalcohol fatty liver (NAFL) to NASH. Immunophenotypically, in addition to the common markers of HCC (glypican-3, heat shock protein-70 [HSP-70] and glutamine synthetase [GS]) ballooned tumor hepatocytes are negative for cytokeratin (CK) 8/18, except for the Mallory-Denk bodies, which are also labeled by ubiquitin. ^{, ,} Additionally, SH-HCCs are diffusely stained with sonic hedgehog ligand, and a minority of them express progenitor markers, including SALL4, EpCAM, and CK19.

Whether SH-HCC may present a better or worse prognosis compared with conventional HCC remains difficult to conclude, because available data are derived from resected or transplanted patients. Nevertheless, nearly all failed to show any statistical difference in terms of overall survival or disease-free survival. ^, Such clinical behavior is supported by the less aggressive histologic phenotype with a lack of satellite nodules and microvascular invasion that SH-HCC seems to display.

Scirrhous HCC.

Scirrhous HCC is a rare (~5% of HCCs) but distinctive variant characterized by abundant, dense fibrous stroma and compressed, sometimes elongated, malignant hepatocytes ( Fig. 87.14 ). The tumor tends to occur in an older age group, affect men and women equally, and might be associated with hypercalcemia. Although generally smaller in size, they exhibit granular eosinophilic cytoplasm, vesicular nuclei, and conspicuous nucleoli. Bile pigment can sometimes be discerned. Scirrhous HCC is characterized by the expression of progenitor markers, including CK19 and CD133 and also demonstrates activation of transforming growth factor-beta (TGF-β) pathway/epithelial-to-mesenchymal transition. ^,

HCC in noncirrhotic liver.

This group encompasses several entities. HCC might develop during the evolution of a chronic fibrosing liver disease, at the stage of incomplete cirrhosis (septal fibrosis). This is especially common in the context of chronic HBV infection and more often reported in patients with nonalcoholic fatty liver disease (NAFLD) given the rising prevalence of metabolic syndrome worldwide. ^{, , ,} Because of the possible reversibility of cirrhosis, it is not known whether HCCs in incomplete cirrhosis develop during an ongoing fibrogenesis or along the reversion of cirrhosis. Finally, HCC may also arise from the malignant transformation of preexisting hepatocellular adenoma (see later) (see Chapter 88A ).

Among HCCs developed in a normal background liver, the fibrolamellar variant was first delineated as a distinct entity in 1980. In a population-based study, fibrolamellar HCC constituted 0.85% of all cases of primary liver cancer and 13.4% of all cases in patients younger than 40 years. Clinically, it occurs in young people with equal sex ratio, and no association with chronic liver disease, cirrhosis, or any other known predisposing risk factors. Characteristic genetic abnormalities have been suggested. ^, In addition, overexpression of neuroendocrine genes, including prohormone convertase 1, neurotensin, delta/notch-like epidermal growth factor–related receptor and calcitonin, has been reported in fibrolamellar HCC. These data are consistent with description of neurosecretory granules in tumoral cells by electron microscopy and may support the potential efficiency of chemotherapeutic and targeted therapies. More importantly, a chimeric transcript resulting from an approximately 400-kilobase deletion on chromosome 19 was specifically identified in a set of fibrolamellar HCCs. The fusion transcript encodes a chimeric protein coupling a segment of the HSP (DNAJB1) with the catalytic domain of protein kinase A. Later, messenger RNA (mRNA) and long intergenic noncoding RNA (lncRNA) signatures, highlighting the key role for protein kinase A signaling, were specifically reported in this subtype.

On gross examination, fibrolamellar HCC is firm, mostly well-defined but unencapsulated single nodule that ranges from 5 cm to over 20 cm. On cut section, the tumor is gray to brown with scalloped borders and a solid consistency ( Fig. 87.15 ). Prominent fibrous septa subdivide the mass and may connect with a central zone of scarring ( Fig. 87.16 ). Such features may be confusing with focal nodular hyperplasia. In addition, there are several reports in the literature of fibrolamellar HCC spatially associated with focal nodular hyperplasia, although filiation between these two lesions have never been convincingly demonstrated. Calcifications may be observed.

The distinctive histologic features are fibrous stroma and large eosinophilic tumor cells ( Fig. 87.17 ). The stroma comprises dense fibrous bands of varying thickness that are organized around nests, cords, and sheets of neoplastic cells. The tumor cells are usually larger than normal hepatocytes and display abundant, granular, and deeply eosinophilic cytoplasm with prominent nucleoli. Bile pigment is common and fat or glycogen accumulation sometimes seen. Most fibrolamellar HCCs are histologically of low grade, mitoses are usually sparse, and nuclear pleomorphism or multinucleation is infrequent. Cytoplasmic inclusions of various types are common, including ground-glass pale bodies, eosinophilic cytoplasmic globules of variable periodic acid–Schiff (PAS) positivity, and, rarely, Mallory bodies (see Fig. 87.17 ). Fibrolamellar HCCs express CK7 abundantly and, in some cells, biliary-type CK19. Interestingly, tumor cells from fibrolamellar HCC also display CD68 positivity with a granular or stippled cytoplasmic staining.

Fibrolamellar HCC tends to be slow-growing and frequently surgically resectable with a better prognosis than other types. Successfully resected patients have a good chance of long-term survival despite extrahepatic recurrences. Transcriptomic data identified two distinct clinical subgroups of fibrolamellar HCC showing different evolutive course. Noteworthy, conventional HCC may display, at varied extent, morphologic features of the fibrolamellar type. Despite the presence of this fibrolamellar component, these so-called mixed-fibrolamellar HCCs (FLC/HCCs) keep clinicopathologic characteristics of conventional tumors, mostly observed in older patients with preferentially liver recurrences. An extensive molecular study recently demonstrated that such mixed FLC/HCCs define a subgroup associated with BAP1 (gene encoding BRCA1-associated protein-1) inactivation related to mutations or translocations. None of them carried the DNAJB1-PRKACA fusion as observed in the fibrolamellar subtype. Compared with conventional HCC, FLC/HCCs are more often observed in women in absence of chronic liver disease but display a poorer prognosis.

Histologic grading

Grading of HCC relies on the Edmondson and Steiner system, which subdivided HCC into four grades, I to IV, on the basis of histologic and cytologic resemblance to normal liver. This grading has been shown to correlate with the DNA content and cellular proliferation indices of the tumor. Grade I is the well-differentiated one, in which hepatocytic-like cells are arranged in thin trabeculae. Small HCCs tend to be grade I, although they are often not uniform in their differentiation. Grade II HCCs are composed of larger tumor cells with abnormal nuclei. Glandular structures may be present. In grade IV, neoplastic cells are much less differentiated with hyperchromatic nuclei and loss of trabecular pattern. In fact, most HCCs present as grade II or III. Therefore, and as for other carcinomas, there is a general tendency to summarize the grading to a three-scale system with well-, moderately- and poorly differentiated HCC. Tumor grade is used to predict patient survival and disease-free survival after resection and liver transplantation as well, with the worst grade tending to drive prognosis. Importantly, grading obtained from the needle biopsy correlates well with the grading performed in the respective resection specimen.

Hepatocellular carcinoma staging

Several staging systems have been proposed for HCC. ^, The main prognostic factors are related to tumor stage (number and size of nodules, presence of vascular invasion, extrahepatic spread), liver function (defined by Child-Pugh class, bilirubin, albumin, portal hypertension), and general health status. Tumor-node-metastasis (TNM) staging takes into account the size of the nodule, presence of vascular invasion, and number of nodules. The cause has not been identified as an independent prognostic factor.

Size is a major prognostic factor. Small or minute carcinomas have a better prognosis, although with larger cancers, the tumor size does not directly correlate with outcome. The presence of satellite nodules around the main tumor has been recognized as a prognostic factor in several studies. Improved survival has been associated with tumors that are encapsulated or fail to invade surrounding hepatic parenchyma.

Macroscopic and microscopic vascular invasion are among the relevant histoprognostic criteria and should be mentioned. Vascular invasion is a known predictor of recurrence and survival, directly associated with histologic differentiation, degree, and size of the main nodule. ^, Characteristically, the prevalence of microscopic vascular invasion increases with tumor size, with up to 60% to 90% in nodules above 5 cm in size.

A major influence on clinical status of the patient is the presence or absence of cirrhosis, which thus becomes a leading indicator for survival (see Chapter 74 ). Therefore simultaneous biopsy of nontumoral liver is of major importance and should be systematically performed to contribute to therapeutic decisions and assist the pathologist in identification of very-well-differentiated HCC.

Premalignant hepatocellular lesions and small hepatocellular carcinoma

From experimental hepatic carcinogenesis and epidemiologic studies, it appears that liver carcinogenesis follows a multistep process. Although a few HCCs arise in normal liver, the vast majority of them develop from the stepwise pathway of normal liver → fibrosis → cirrhosis → HCC. Therefore cirrhosis is recognized as a precancerous condition.

There is consensus to support that HCC results from cumulative genetic and epigenetic events that may differ according to the cause of the chronic background liver disease. Although recurrent gene abnormalities have been reported in fully developed HCC, there is a paucity of knowledge regarding the early molecular events associated with HCC (see Chapter 9B ).

Several studies using different approaches have looked for early molecular abnormalities in regular cirrhosis. Molecular markers have been evaluated in macronodules and none of the oncogenes or tumor suppressor genes involved in advanced HCC have been repeatedly found altered in the precancerous lesions. By contrast, proliferation markers, neoangiogenesis, telomerase expression, allelic losses, and clonality have been studied with more consistent results. Interestingly, using clonal analysis these studies convincingly demonstrated that among cirrhotic micronodules that appear similar on light microscope, some are already monoclonal (neoplastic) and other polyclonal (regenerative). ^, Telomerase, an enzyme that allows unrestricted cell proliferation and is specifically expressed in cancer, can be detected in some but not all of these clonal micronodules without any remarkable histopathologic features. More recently, TERT promoter mutations have been reported as the most frequent mutations in liver carcinogenesis, with an increasing rate from dysplastic nodules (<20%) to HCC (~60%).

Morphologically, several terms have been used in the past to define the intermediate lesions such as adenomatous hyperplasia and atypical adenomatous hyperplasia, but in 1995 the International Working Party proposed a unified nomenclature that has gained wide acceptance and is still currently used. This classification was recently reviewed and completed by an international group that added to the panel definitions of the early and small HCC.

Macroregenerative nodule.

Macroregenerative nodules (MRNs) are tumor-like hepatocellular masses that can arise in the setting of cirrhosis. These lesions have increasingly been detected resulting from both improved radiographic imaging techniques and more widespread screening of cirrhotic patients. Most MRNs are large, discrete nodules ranging from 1 to 3 cm in diameter. There is no minimum size threshold for definition because MRNs have to be appreciated according to the size of background cirrhotic nodules (2-fold to 3-fold larger than cirrhotic nodules). ^, Macronodules are often well-limited and surrounded by condensed connective tissue ( Fig. 87.18 ). MRNs are common; they have been found after careful inspection in about 10% of cirrhotic livers at autopsy or at time of transplantation. Histologically, most MRNs are indistinguishable from the usual parenchymal nodules seen in cirrhosis. Normal-appearing hepatocytes are arrayed in plates of one or two cells thickness limited by a regular sinusoid lining and bounded by typical fibrous septa containing blood vessels, bile ductules, and varying degrees of inflammatory infiltration.

Dysplastic nodule.

Dysplastic nodules (DNs) are sizable lesions arising in cirrhosis that differ from the surrounding liver parenchyma in size, color, texture, and degree of bulging of the cut surface. Based on microscopic features, DNs are further subdivided into low grade (LG-DN) and high grade (HG-DN), the latter being closer to HCC in the spectrum of hepatocarcinogenesis. ^{, ,} Briefly, LG-DNs display features suggestive of a clonal cell population but lack architectural atypia whereas HG-DNs show cytologic and architectural atypias but insufficient for a diagnosis of malignancy ( Fig. 87.19 ). Although dynamic imaging may help differentiate DNs from small HCCs, liver biopsy remains the gold standard.

The premalignant nature of DN is supported by different clues, including the common association with HCC in resected and explanted end-stage cirrhotic livers, with the presence of hepatocellular cytoarchitectural abnormalities featuring a lesion on the way to HCC ; the morphologic evidence of neoangiogenesis under the form of unpaired arteries supporting the abnormally ongoing vascular supply ^, ; and the detection of both genetic and epigenetic changes greater than those in the surrounding tissues but less frequent and consistent than in HCC; and their natural history showing an increased risk for malignant transformation compared with control cirrhotic nodules. ^, Among the various cytologic alterations that characterized DNs are enlarged, crowded, or irregular nuclei with patent nucleoli, increased nuclear-to-cytoplasmic ratio ( Fig. 87.20 A–B). Atypical architectural findings involve expansile proliferative zones sometimes located within an MRN (nodule-in-nodule formations), increased number of unpaired arteries, focal loss of associated reticulin framework, and foci of abnormal structural patterns, including irregular thickening of the hepatic plates (see Fig. 87.20 C). Stromal invasion, defined as the presence of tumor cells invading into the portal tracts or fibrous septa, is, according to Eastern pathologists, the most relevant feature in discerning HG-DN from small HCCs (see Fig. 87.20 D). The degree and extent of these features vary greatly among cases, thus forming a histologic continuum that stretches between ordinary macroregenerative nodules and obvious HCC. Immunohistochemical markers such as glypican 3, HSP-70, GS, and arginase-1 have been recently evaluated. Alone or in combination, they have good accuracy to discriminate HCC from precancerous lesion in surgical specimens but also in liver biopsy.

DNs must be differentiated from dysplastic foci, which are defined as microscopic changes incidentally recognized in cirrhotic tissue. According to histopathologic criteria, dysplastic foci are split into large or small liver cell changes (see Fig. 87.20 A–B). Although large liver cell change (previously large liver cell dysplasia) consists of abnormal but nonneoplastic hepatocytes that are a predictor of HCC development, small liver cell change is composed of neoplastic cells that are direct precursors of HCC. ^,