Liver Neoplasms

Gross Findings

Hepatic adenoma is a well-circumscribed, often subcapsular mass in the right lobe of an otherwise noncirrhotic liver. Ruptured HAs may be obscured by blood clot and difficult to recognize, but the tumor is usually pale or more yellow compared with the adjacent liver ( Fig. 18.3 ). Fibrous septa may be present as a result of a previous infarct.

Microscopic Findings

On first glance, most HAs represent a nodular proliferation of bland-appearing hepatocytes arranged in cords that are one to two cells thick and separated by sinusoids lined by inconspicuous Kupffer cells. However, no normal portal tracts are present, and there is a notable lack of any biliary epithelium. Another key feature of HA is the presence of haphazardly distributed arteries and thin-walled veins ( Fig. 18.4 ). Hepatocellular rosettes (pseudoglands) are rare in HA and should not be confused with bile ducts. Extensive pseudoglandular proliferation raises concern for a diagnosis of well-differentiated HCC.

The hepatocytes of HA frequently display clear or vacuolated cytoplasm because of accumulation of glycogen or fat. Cytoplasmic inclusions representing α1-antitrypsin (α1AT), megamitochondria, and Mallory’s hyaline are occasionally found. Focal cellular pleomorphism and prominent nucleoli may be seen, especially in tumors associated with androgenic steroid use. Mitoses, vascular invasion, and stromal invasion are not seen in HA and are suggestive of malignancy. Various degenerative changes occur in HA and include dilated sinusoids and larger blood-filled (peliosis-like) spaces, myxoid stroma, and areas of necrosis, infarct, and hematoma.

The current World Health Organization (WHO) classification of HAs is based on genotype-phenotype correlation. Based on presence of HNF1α or β-catenin mutation and expression of SAA or CRP in tumors that show a conspicuous inflammatory infiltrate, HAs can be subclassified into four categories: (1) HAs with mutations of the HNF1α gene; (2) HAs with β-catenin gene mutation; (3) inflammatory HA positive for serum amyloid A (SAA) or CRP; (4) sonic hedgehog HA harboring somatic deletions of inhibin subunit beta E ( INHBE ) leading to INHBE and GLI-1 fusions; and (5) unclassified HA, tumors that do not fit any of these categories ( Table 18.2 ). HNF1α -inactivated tumors are the second most common (30%–35% of HAs) and show prominent steatosis without cellular atypia or inflammation ( Figs. 18.5A and B ). β-catenin–activated HA (10%–15%) is more common in male patients and tend to show cytologic and architectural atypia, overlapping features between HA and HCC. Inflammatory HAs are the most frequent (35%–40%) and show pseudoportal tracts, bile ductular proliferation, inflammatory infiltrates, and prominent sinusoidal dilation (telangiectatic areas) ( Figs. 18.5 C and D ). Lesions previously classified as “telangiectatic FNHs” are now classified as inflammatory HA based on clonality studies and expression of SAA and CRP. A new subtype has been described recently that shows activation of the sonic hedgehog pathway caused by INHBE deletion and consequent INHBE-GLI-1 fusion. This subtype confers an increased high risk of hemorrhage, even in small tumors.

The term adenomatosis is sometimes used for cases with multiple (>10) adenomas. Because the etiologic associations appear to be similar for multiple and solitary adenomas, distinction between these two groups is probably not warranted on clinicopathologic grounds. HNF1A and inflammatory HA are the most common subtypes that may present with adenomatosis. It is also important to remember that different HA subtypes may occur in the same liver.

Gross Findings

Hepatocellular carcinoma arising in a noncirrhotic liver usually grows as a single large mass with or without satellite nodules ( Fig. 18.8A ) and may also exhibit this pattern in the setting of cirrhosis. However, tumors arising in cirrhosis may grow as numerous small nodules (diffuse type) that may be difficult to distinguish from the background liver ( Fig. 18.8B ). Tumor nodules are soft, bile stained, or yellow to tan and often variegated because of foci of hemorrhage and necrosis. Separate tumor nodules may represent multicentric growth or may represent tumor spread via intrahepatic vascular routes. Macroscopic portal vein, hepatic vein, or bile duct invasion are present in some cases ( Fig. 18.8C ). Involvement of the inferior vena cava, sometimes with extension into the right atrium, may be found.

Microscopic Findings

Hepatocellular carcinomas show a wide range of differentiation, and several grades may be present within the same tumor. Well-differentiated HCC shows obvious hepatocellular differentiation with tumor cells arranged in a trabecular pattern lined by endothelial cells. Stroma is typically scant, and bile production by neoplastic cells is pathognomonic of HCC but should not be confused with bile production by trapped non-neoplastic hepatocytes. Cytoplasmic inclusions such as Mallory’s hyaline, α1AT inclusions, and fat accumulation are frequently present, often in focal areas of the tumor or in individual tumor nodules. Vascular lakes may simulate peliosis hepatis. The WHO classification divides HCC into well-, moderately, and poorly differentiated grades. Whereas well-differentiated tumors show minimal atypia and resemble normal hepatocytes, poorly differentiated tumors resemble a variety of carcinomas and are not clearly recognizable as hepatocellular on H&E stain. The moderately differentiated spectrum of tumors falls between the two extremes. In the compact or solid areas, compression of broad trabeculae forms sheets with inconspicuous sinusoids ( Fig. 18.9A ). Pseudoglandular (acinar) formation with dilated rounded spaces rounded by cytologically malignant hepatocytes may be mistaken for adenocarcinoma ( Fig. 18.9B ). The lumen of these acini may contain bile.

Among the major histologic subtypes are steatohepatitic, clear cell, macrotrabecular massive, scirrhous, chromophobe, neutrophil-rich, lymphocyte-rich, and fibrolamellar hepatocellular carcinoma (FL-HCC). The steatohepatitic subtype (5%–20%) reveals steatosis and ballooning as seen in steatohepatitis ( Fig. 18.9D ). Because of the fragmentation of the reticulin framework in areas of fat, the differential diagnosis can be challenging. Clear cell HCC (3%–7%) demonstrates clear cell morphology in more than 80% of the tumor ( Fig. 18.9E ) and carries better prognosis than conventional HCC. Macrotrabecular massive HCC (5%) consists of thickened trabeculae larger than 10 cells thick and has worse prognosis than conventional HCC ( Fig. 18.9F ). The rare scirrhous HCC (4%) displays prominent fibrous stroma accounting for more than 50% of the tumor ( Fig. 18.9G ). Neutrophil-rich (<1%), chromophobe (3%), lymphocyte-rich (<1%) ( Fig. 18.9H ), sarcomatoid ( Fig. 18.9I ), lipid-rich, HCC with syncytial giant cells ( Fig. 18.9J ), GCSFP producing HCC, and cirrhotomimetic are rare subtypes.

Immunohistochemistry

Hepatocellular carcinoma demonstrates canalicular staining pattern with antibodies to CD-10 and polyclonal carcinoembryonic antigen (CEA) ( Fig. 18.10 ), as well as positivity for hepatocyte (HepPar-1), glypican 3, and Arginase-1. Granular cytoplasmic staining pattern with HepPar-1 and nuclear/cytoplasmic staining for Arginase is present in HCC and normal hepatocytes. Glypican 3 is expressed in HCC (with lower sensitivity in well-differentiated HCC) and negative in nonmalignant liver. Arginase-1 has been proposed as the hepatocellular marker with greater sensitivity in poorly differentiated HCC. In situ hybridization for albumin messenger RNA appears to be highly sensitive but not specific because it has been demonstrated in CCs and adenocarcinomas of other sites.

Even though CAM 5.2 is positive in HCC, other keratins (CK7, CK20, CK19, AE1/AE3, Ker 903) area variable expressed and more commonly negative. CK19 expression has been associated with a poor prognosis.

MOC-31 and Ber-Ep4 are negative and can be useful in the differential diagnosis with CC or other adenocarcinomas.

Gross Findings

Most FL-HCCs arise in the left lobe, but large tumors may affect both lobes. The tumors are usually solitary, firm, and well circumscribed and may be bile stained, necrotic, or hemorrhagic. They are typically large, measuring up to 25 cm. A central stellate scar similar to that seen in FNH may be present ( Fig. 18.12 ). The adjacent non-neoplastic liver is unremarkable.

Microscopic Findings

The tumor cells of FL-HCC are very large, display abundant granular eosinophilic cytoplasm because of large numbers of mitochondria and distinct cell borders, and have a distinctive oncocytic appearance ( Fig. 18.13A ). A defining feature of FL-HCC is the presence of parallel bands of hyalinized fibrous tissue separating the tumor cells into nests ( Fig. 18.13B ). Other patterns of fibrosis include haphazard collagen deposition and tumors showing areas with little or no intratumoral fibrosis (least common pattern). Cytoplasmic eosinophilic hyaline globules, which may be Periodic Acid–Schiff (PAS) positive and diastase resistant, may represent α1AT. Cytoplasmic pale bodies contain fibrinogen and are present in about 50% of cases ( Fig. 18.13C ). In a subset of cases, pseudoglandular formation and mucin production can be seen, but these findings do not constitute a component of adenocarcinoma. Most FL-HCC are moderately differentiated, but they can contain foci of carcinoma that are poorly differentiated. In addition to staining with HepPar-1, albumin in situ hybridization (ISH), and arginase-1, FL-HCC is positive for CK7 ( Fig. 18.13D ) and CD68 ( Fig. 18.13E ). Polyclonal CEA demonstrates a canalicular staining pattern.

Recent molecular data have shown that FL-HCC show activation of protein kinase A, most commonly through a DNAJB1-PRKACA fusion transcript, secondary to somatic intrachromosomal deletion on chromosome 19. This genetic abnormality is diagnostic of FL-HCC in the differential of hepatocellular malignancies. Interestingly, the DNAJB1-PRKACA fusion transcript has been also demonstrated in other oncocytic pancreatic and biliary neoplasms, but these are typically not in the differential of FL-HCC so do not constitute a diagnostic challenge.

Ultrastructural Findings

The cytoplasm contains numerous mitochondria, as expected from the oncocytic appearance of the tumor cells. Dense core neuroendocrine-like granules may also be rarely found.

Gross Findings

Hepatoblastoma is typically a solitary mass that may be quite large, measuring up to 20 cm. Purely epithelial hepatoblastoma is a soft, fleshy mass ( Fig. 18.14 ); whereas the fetal type grossly appears similar to normal liver, other patterns show a variegated appearance. Tumors with a prominent mesenchymal component are often firm and may be calcified. Cystic degeneration, necrosis, and hemorrhage may be seen.

Microscopic Findings

Hepatoblastomas may be classified as either epithelial or mixed epithelial–mesenchymal and are subclassified into a variety of patterns that are usually present in variable combinations ( Figs. 18.15A-D ).

• 1.

  Fetal pattern (30%): Hepatocytes are uniform and similar to normal hepatocytes, although they have a slightly higher nuclear-to-cytoplasmic ratio. An alternating light and dark pattern is characteristic on low power. Mitoses are rare and less than 2 per 10 hpf. The tumor cells form cords two to three cells thick, separated by sinusoids, in a pattern reminiscent of normal liver. However, normal structures such as portal tracts, bile ducts, and ductules are absent. A mitotically active aggressive variant of the fetal type is also recognized.

• 2.

  Embryonal pattern (20%): The tumor cells in the embryonal pattern are less differentiated and cohesive than the fetal pattern and have a high nuclear-to-cytoplasmic ratio and coarser chromatin. The trabecular pattern is not well developed, and the tumor cells may form sheets. Mitoses and necrosis are more common than in the fetal pattern.

• 3.

  Macrotrabecular pattern (3%): This pattern is characterized by broad trabeculae 10 or more cells thick. Trabeculae may be composed of embryonal or fetal cells.

• 4.

  Small cell undifferentiated pattern (3%): This pattern is the least differentiated pattern and resembles other small blue cell tumors of childhood. The tumor is composed of loosely cohesive sheets of uniform small cells with scanty cytoplasm. The tumor cells are positive for keratins.

• 5.

  Cholangioblastic pattern (rare): Small ducts are dispersed around or within a hepatocellular component.

• 6.

  Mixed epithelial and mesenchymal pattern (44%). Both epithelial and mesenchymal differentiation are present. The primitive mesenchymal component may be primitive, with spindle or stellate cells with little cytoplasm, or display differentiation along chondroid and rhabdomyoblastic lines. Osteoid is the most frequent heterologous element and may be more prominent after chemotherapy. The mesenchymal elements may also be keratin positive, suggesting sarcomatoid differentiation of the epithelial component.

• 7.

  A subtype of mixed pattern tumors displays teratoid features and may contain elements of mature teratoma such as keratinized squamous epithelium, intestinal epithelium, and neuroectodermal structures.

Immunohistochemistry

Positivity for keratins helpful in confirming epithelial differentiation. Markers of hepatocellular differentiation are useful in fetal, embryonal, and small cell undifferentiated subtypes; the latter may be negative for HepPar-1 but may be positive for arginase 1 and glypican 3. INI-1 loss is seen in a subset of small cell undifferentiated subtype of tumors that are associated with a worse prognosis.

Gross Findings

Bile duct hamartomas appear as single or multiple subcapsular, gray-white, or occasionally green nodules smaller than 0.5 cm in diameter.

Microscopic Findings

Bile duct hamartomas are found directly adjacent to portal tracts and consist of ectatic, branched bile ducts lined by a single layer of bland, low columnar to cuboidal biliary epithelium ( Fig. 18.16 ). The lumen frequently contains bile. The stroma is dense and hyalinized, with minimal inflammation.