Benign and Malignant Tumors of the Liver
Linda D. Ferrell
Introduction
Primary tumors of the liver are classified as benign and malignant epithelial and nonepithelial neoplasms. The most common are epithelial neoplasms, which are predominantly hepatocellular and bile ductular types. Other non-neoplastic tumor-like lesions are of clinical significance. The 2010 classification scheme of the World Health Organization (WHO), which includes neoplasms and tumor-like lesions, is provided in Table 55.1.1 The nomenclature used in this chapter follows these recommendations.
Table 55.1
World Health Organization Classification of Primary Liver Tumors and Tumor-Like Lesions
| Epithelial Tumors or Tumor-Like Lesions | Nonepithelial Tumors or Tumor-Like Lesions |
| Benign | |
| Hepatocellular adenoma | Cavernous hemangioma |
| Focal nodular hyperplasia | Angiomyolipoma |
| Bile duct adenoma | Infantile hemangioma |
| Bile duct hamartoma | Lymphangioma |
| Microcystic adenoma | Mesenchymal hamartoma |
| Biliary adenofibroma | Inflammatory pseudotumor |
| Solitary necrotic nodule | |
| Premalignant or Precursor Lesions | |
| Dysplastic nodule | |
| Low-grade | |
| High-grade | |
| Mucinous cystic neoplasms, low and high grade | |
| Intraductal papillary neoplasms, low and high grade | |
| Malignant | |
| Hepatocellular carcinoma, including fibrolamellar variant | Angiosarcoma Epithelioid hemangioendothelioma Embryonal (undifferentiated) sarcoma Lymphoma and other hematopoietic tumors |
| Cholangiocarcinoma, peripheral, hilar, and extrahepatic types | |
| Mucinous cystic neoplasm with invasive carcinoma | |
| Intraductal papillary neoplasm with invasive carcinoma | |
| Malignancies of Mixed or Uncertain Origin | |
| Combined hepatocellular carcinoma and cholangiocarcinoma | Kaposi sarcoma Leiomyosarcoma Rhabdomyosarcoma Synovial sarcoma Germ cell tumors (teratoma, yolk sac tumor) |
| Hepatoblastoma | |
| Carcinosarcoma | |
| Calcifying nested epithelial stromal tumor | |
| Malignant rhabdoid tumor | |
Data from Bioulac-Sage P, Balabaud C, Wanless I, et al. Tumours of the liver and intrahepatic bile ducts. In: Bosman F, Carneiro F, Hruban R, Theise N, eds. WHO Classification of Tumours of the Digestive System. Lyon, France: IARC; 2010:195-261.
Specimen Analysis
Documentation
Verification of tumor type and status as a primary or metastatic neoplasm or as a non-neoplastic tumor is the most important consideration in the diagnosis. Descriptive comments should focus on information important for tumor staging, such as tumor size (smaller or larger than 5 cm for hepatocellular carcinoma [HCC]), number of lesions (single or multiple), specific lobes or segments involved, local extension of the lesion outside of the liver, and presence or absence of gross vascular invasion, and it should include notation regarding which of the major vessels (portal or hepatic vein) are involved.
Microscopic evaluation should involve adequate numbers of sections relative to tumor size to assess vascular invasion or extension outside of the Glisson capsule.2,3 Sections near the edge of the tumor are recommended for detection of vascular invasion if gross invasion is not seen. Gross observation of possible large vessel invasion should be documented microscopically. A section of non-neoplastic liver should be included for identification of the background pathology. Table 55.2 delineates tumor (T) staging for HCC by the Union for International Cancer Control and American Joint Committee on Cancer (UICC/AJCC) recommendations (http://www.uicc.org). Metastasis (M) and node (N) staging consist of X for not known, 0 for absent, and 1 for present.
Table 55.2
Primary Tumor Staging for Hepatocellular Carcinoma
| Tumor Stage | Definition |
| TX | Primary tumor cannot be determined |
| T0 | No evidence of primary tumor |
| T1 | Solitary tumor without vascular invasion |
| T2 | Solitary tumor with vascular invasion or multiple tumors, none >5 cm |
| T3a | Multiple tumors, any >5 cm |
| T3b | Single or multiple tumors of any size involving a major branch of hepatic or portal vein |
| T4 | Tumor invading adjacent organs (other than gallbladder) or perforating visceral peritoneum |
In typical situations, the surgical margins of the resection specimen should be inked before the tumor is sectioned for definitive evaluation of the distance from the margin to the tumor, and the status of the resection margins should be included in the report. Some studies suggest that a tumor-free margin of at least 1 cm is directly related to a better prognosis for some types of malignant tumors.4 Other studies have shown that a wide resection is preferable to a limited excision when the HCC is small.3 The distance from the tumor to the closest margin of resection should be documented clearly in the pathology report.
Biopsy Methods
Small-core and fine-needle aspiration biopsies (FNABs) may be used to diagnose specific tumor types (see Chapter 45). The accuracy of FNABs is enhanced by the use of extra tissue preparations, such as cell buttons, for evaluation of the histologic features of tissue sections obtained from the FNAB material.5 This method is especially helpful to evaluate well-differentiated hepatocellular lesions, in which subtle cytologic features such as cell size, crowding of nuclei, and increased nucleus-to-cytoplasm ratio or architectural features such as formation of trabeculae or width of cell plates may be difficult to assess with smears alone. In these instances, use of histologic sections in combination with well-prepared smears can be successful to distinguish well-differentiated HCC from other lesions such as hepatocellular adenoma, focal nodular hyperplasia, macroregenerative nodules, or high-grade dysplastic nodules. Preparation of cell buttons, particularly in cases of poorly differentiated neoplasms or tumors with unusual morphology, may result in a more accurate diagnosis through the application of immunohistochemical techniques.
Because the amount of biopsy material is often limited, slides of unstained material should be prepared when the tissue block is initially sectioned to ensure that sufficient material is available for additional levels or stains. The usual panel of stains, which includes trichrome, reticulin, periodic acid–Schiff with diastase digestion (d-PAS), and iron stain, should not be ordered automatically at the time of gross examination, because excess sectioning (before examination of the hematoxylin and eosin–stained slides) may deplete the tissue block of diagnostic material that should be available for other diagnostic stains that are determined later.
Hepatocellular Tumors
Hepatocellular Adenoma
Clinical Features
In the past, hepatocellular adenomas (HCAs) were considered rare tumors that developed almost exclusively in young women during their reproductive years and only rarely occurred in men6,7 or children.8 However, the incidence is increasing, mostly because of the obesity epidemic, and lesions are seen in older women (40 to 50 years) and in men.1
Most patients have an abdominal mass, but some also have abdominal pain, discomfort, or nausea. Radiographically, most HCAs exhibit an enhanced vascular pattern. A significant proportion manifest with hemoperitoneum.9 Lesions larger than 5 cm in diameter usually are associated with a higher risk of hemorrhagic complications, and resection is typically recommended for these lesions. The serum alkaline phosphatase level may be elevated, but serum α-fetoprotein (AFP) levels are usually normal or only minimally elevated.
Pathogenesis
HCAs have historically developed as a result of oral contraceptive10 or anabolic steroid use. However, low-dose estrogens are now widely used, and the incidence of HCAs related to oral contraceptives may be decreasing. Some HCAs associated with oral contraceptive use regress after cessation of the drugs, but others do not.
Other risk factors for the development of adenomas include obesity (and probably the metabolic syndrome) and metabolic disorders, especially the carbohydrate metabolic disorders such as glycogen storage diseases I and IV, galactosemia, tyrosinemia, and familial diabetes mellitus.11 The consensus of the International Working Party is that a diagnosis of HCA should not be assigned for a lesion that arises in a cirrhotic liver unless regression is evident when the stimulus is removed or unless one of the risk factors is discernable.12 HCCs may arise within HCAs (see Chapter 44).10,13
Genetic and molecular analyses have resulted in the subclassification of HCA into four major groups (Table 55.3) (see Chapter 44).14 The first group demonstrates hepatocyte nuclear factor 1α (HNF1A) inactivation mutations that are somatic or germline. These tumors are characterized by steatosis, and they tend to occur in younger patients, some of whom have diabetes. Patients frequently have a history of familial adenomatous polyposis. The second major group of HCAs has β-catenin mutations. Tumors in this group tend to occur more in males, may have more cytologic abnormalities, exhibit a focal acinar pattern, and are less steatotic. This group is more frequently associated with the development of HCC.15 The third group known as inflammatory HCAs (previously known as telangiectatic or variant HCA and originally described as telangiectatic focal nodular hyperplasia16,17) is characterized by sinusoidal dilation, inflammatory infiltrates, and a focal ductular reaction. The fourth group consists of the remaining HCAs, which are heterogeneous, lack HNF1A or β-catenin mutations, atypical histologic features, and a telangiectatic pattern of growth.
Table 55.3
Hepatocellular Adenoma Variants
| HCA Variant Type | Routine Histologic Features | Immunohistochemical Staining | Clinical Associations |
| HNF1A inactivated | Diffuse fatty change; irregular borders | LFABP1 negative | Maturity onset diabetes of the young (type 3). Adenomatosis is common; risk for HCC low |
| β-Catenin mutated | Focal features overlapping those of well-differentiated HCC such as pseudogland (acinar) formation and/or cytologic atypia | β-Catenin nuclear staining and diffuse GS staining | Male gender and anabolic steroid more common. Variant with most risk for HCC |
| Inflammatory | Dilated sinusoids, fatty change may be focal; stromal/vascular zones with clusters of small arteries, inflammatory cells and peripheral ductular reaction | CRP and SAA demonstrate diffuse cytoplasmic staining; about 10% may have β-catenin mutations; CK7 highlights ductular reaction but often will not stain as intensely as normal ducts | Obesity very typical association; can be seen in men or women; adenomatosis also common; more difficult to identify by gross appearance |
CK, Cytokeratin; CRP, C-reactive protein; LFABP1, liver-type fatty acid binding protein 1; GS, glutamine synthetase; HCA, hepatocellular adenoma; HCC, hepatocellular carcinoma; HNF1A, hepatocyte nuclear factor 1α; SAA, serum amyloid A.
Pathologic Features
Adenomas may be single or multifocal, and when they are multifocal (>10 lesions),1,14 the condition is referred to as hepatocellular adenomatosis. In most cases, these tumors occur in histologically normal or almost normal livers.12 Adenomas usually are round tumors that tend to bulge on cut section. They are soft and typically somewhat lighter in color than the surrounding liver parenchyma, but their appearance may vary if necrosis or hemorrhage exists. The inflammatory variants can be very ill defined and are notable only in some cases by an increased congestive appearance, some bulging, or bogginess of the parenchyma. HCAs usually lack significant fibrosis or nodularity, although these features are rarely present.13 Normally, HCAs are not encapsulated and can have an irregular, ill-defined border, especially in the inflammatory forms. Rarely, HCAs may have a slate gray to black color caused by large amounts of lipofuscin pigment, which is sometimes referred to as black adenoma.11
Microscopically, HCAs are composed of a relatively uniform population of hepatocytes arranged in cell plates one to three cells thick (Fig. 55.1). The cell plates usually have a slightly more irregular pattern than those in normal liver. A key feature of HCAs is that the reticulin framework of the cell plates is intact or only focally decreased (Fig. 55.2). The tumor cells are usually similar in size to normal hepatocytes, although they may be slightly smaller or larger. However, the nucleus-to-cytoplasm ratio of adenoma cells is usually the same as for normal hepatocytes. The cytoplasm of tumor cells may be eosinophilic or clear, or it may contain fat droplets, bile stasis, lipofuscin pigment, or Mallory hyaline (rare). The HNF1A-inactivated HCA has a diffuse fatty change, and these lesions also show lack of staining for liver-type fatty acid binding protein 1 (LFABP1) (Fig. 55.3). Other mild variations in cellular morphology, such as multinucleated tumor cells, or rare atypical or pleomorphic hepatocytes may also be seen, but they are usually focal and few in number. Regardless of the cellular morphology, mitotic figures are typically absent or rare in HCAs.
Variations in architecture, such as the formation of acini (i.e., pseudoglands or glandlike structures composed of hepatocytes) may be seen but are typically limited in number. However, this can be a more prominent feature in the HNF1A-inactivated variant and acinar structures may contain bile. Alterations in the sinusoids may appear compressed, resulting in a somewhat uniform and solid appearance of the tumor. Alternatively, peliosis hepatis and sinusoidal dilation may be identified in some adenomas, particularly the inflammatory variant (see Fig. 55.1). Large arterial vessels often are prominent in all forms, and multiple, small arteries in clusters surrounded by mild inflammatory cell infiltrates are common features of the inflammatory variant. The inflammatory variant exhibits diffuse immunostaining for inflammatory proteins, including C-reactive protein (CRP) and serum amyloid A (SAA) (Fig. 55.4).
Kupffer cells may be seen in these adenomas, but fewer are identified than in normal liver. Rarely, a partial capsule exists, showing foci of tumor cells that merge with adjacent liver parenchyma at sites where the capsule is absent (see Fig. 55.3). A bile ductular reaction is typically absent, but in the inflammatory type, a ductular reaction at the periphery of the arterial foci may simulate portal tracts. Portal tracts are occasionally found within HCAs at the border of the lesions. Areas of infarction and hemorrhage are relatively frequent findings, especially in larger lesions.
The mutated β-catenin variant demonstrates focal positive hepatocellular nuclear immunostaining for β-catenin (Fig. 55.5) and diffuse staining for glutamine synthetase. This type is most likely associated with anabolic steroid use and is more likely to show nuclear atypia, peliosis hepatis, or a prominent acinar (pseudoglandular) pattern.11,12 However, it is controversial whether some of these lesions represent well-differentiated HCCs. It is prudent to consider anabolic steroid–related lesions with atypia as well-differentiated hepatocellular neoplasms of uncertain malignant potential, and most authorities recommend resection of all β-catenin–mutated lesions, regardless of size.
Differential Diagnosis
The main differential diagnoses for HCA are focal nodular hyperplasia (FNH) and well-differentiated HCC (see Table 55.4). Adenomas normally have a relatively uniform cell population that resemble normal liver, lack mitotic activity, reveal cell plates less than three cells thick, and have an intact reticulin framework lining the cell plates. These features help to distinguish this lesion from well-differentiated HCC. If a lesion shows more than rare cytologic atypia or focal loss of reticulin pattern, particularly in a male patient or older woman, a diagnosis of well-differentiated HCC or well-differentiated hepatocellular neoplasm of uncertain malignant potential should be considered.
HCAs stain positively for hepatocellular markers, such as the cytokeratin marker CAM 5.2 and the canalicular marker polyclonal carcinoembryonic antigen (CEA). Adenomas often show CD34 positivity in the endothelial cells that line the cell plates, similar to that seen in HCC. This marker cannot be used reliably to distinguish HCA from HCC.18 Staining for AFP is typically negative in HCAs, but because it is often negative in well-differentiated HCC, use of this marker is not typically helpful. Staining for glypican 3 (GPC3), an oncofetal protein, is negative in typical HCAs, and it is more often positive in HCCs than AFP staining.19,20 However, GPC3 is less useful in distinguishing very-well-differentiated HCCs from HCA, because the two may have similar (negative) staining patterns.21,22
For differentiation of HCA from FNH, isolated arteries in small clusters with limited periarterial stroma, the lack of fibrous bands or central fibrous zone, and lack of nodularity are the most helpful features supporting a diagnosis of adenoma. Ductular reaction at the edge of the fibrous or hepatocyte zones is more prominent in FNH, but some degree of ductular reaction is typically seen in inflammatory HCAs. Acinar formation in HCA must not be confused with bile ductules.
Immunohistochemistry can be helpful to distinguish HNF1A-inactivated HCAs and inflammatory variants of HCA from FNH. Staining for LFABP1 is negative in the former (see Fig. 55.3), and staining for SAA or CRP is diffusely positive in the latter (see Fig. 55.4). Staining of SAA and CRP can be seen in FNH, but it should be focal rather than diffuse. Glutamine synthetase immunostaining in FNH produces a different pattern of staining (discussed later) than that seen in HCAs, which show no significant staining, limited perivenular staining, or diffuse strong staining (e.g., in β-catenin–mutated HCAs).22
Treatment
Surgical excision is justified, particularly for large lesions (>5 cm), because of the risks of tumor growth, life-threatening hemorrhage, the rare development of HCC, and because it is difficult to differentiate an HCA from a well-differentiated HCC. Liver transplantation may be considered for patients with adenomatosis.13
Focal Nodular Hyperplasia
Clinical Features
FNH is a benign, non-neoplastic lesion most commonly encountered in young women,7,9 although significant numbers are seen in men. Classic FNH is often an incidental finding, but it may also come to clinical attention because of its large size (which rarely results from hemorrhage).23 Some patients have abnormal liver function test results, such as elevated γ-glutamyltranspeptidase activity.23
Nodules similar to FNH nodules have been described adjacent to hemangiomas. Some patients with multiple FNH syndrome have at least two FNH lesions associated with one or more other lesions, such as hepatic hemangioma, an arterial structural defect, vascular malformation, meningioma, or astrocytoma.12 Nodules with FNH-like changes are commonly seen in Budd-Chiari syndrome24,25 and in hereditary hemorrhagic telangiectasia (i.e., Rendu-Osler-Weber disease). Many refer to these lesions as “regenerative nodules”6 or as FNH-like lesions.
Pathogenesis
Unlike HCA, FNH does not develop as a result of oral contraceptive use; however, evidence suggests that FNH lesions may increase in size with contraceptive use or regress after cessation of therapy. The exact pathogenesis is not established for FNH, but FNH is thought to represent a hyperplastic or altered growth response to alterations in parenchymal blood flow that occur around preexisting vascular malformations.26 The presence of numerous abnormal muscular vessels in FNH and the association of some of these lesions or similar hyperplastic foci with hemangiomas and the Budd-Chiari syndrome lend support to this theory. Another theory suggests that the lesions result from vascular occlusive events with the formation of collaterals and secondary reactive or ischemic changes.27 Lesions caused by vascular occlusive events may be referred as “FNH-like lesions” (my preferred nomenclature) instead of FNH because they have different etiologic factors and because FNH-like lesions may not have all the typical features of FNH.
FNH has no known malignant potential, and despite its rare association with fibrolamellar HCC, most authorities think that the lesion does not progress to carcinoma. Instead, the association of FNH with fibrolamellar HCC may represent a hyperplastic response to increased vascularity, which is typical of carcinomas. The lesion formerly known as the “telangiectatic” type of FNH, which was originally associated with the multiple FNH syndrome,11 is now recognized as the inflammatory variant of HCA (see Hepatocellular Adenoma, earlier).14
Pathologic Features
Similar to HCAs, FNH usually involves a solitary nodule, but it may be multifocal.12,23 FNH has a nodular appearance, which may simulate the appearance of macronodular cirrhosis, and it tends to be lighter in color than the surrounding liver parenchyma. These lesions are often located near the liver capsule, which may impart a localized nodular appearance mimicking cirrhosis. Occasionally, FNH may be pedunculated. The edges of FNH are normally well demarcated from the normal liver parenchyma, but a fibrous capsule is usually absent. FNH may vary considerably in size. Most FNH lesions have a central fibrous scar, which consists of fibrovascular tissue, not dense scar tissue.
Microscopically, the classic type of FNH is composed of normal-appearing hepatocytes arranged in incomplete nodules and partially separated by fibrous tissue that extends outward from the central fibrous zone of the tumor. Variable numbers of bile ductular structures are normally seen in the fibrous stroma and particularly at the edge of the nodules. The cell plate architecture is similar to that of normal liver. However, the cell plates are usually wider (two to three cells thick), similar to regenerative nodules. The reticulin framework should be intact, but in some lesions, cell plates may have a more acinar appearance, may be wider than three cells (usually not thicker than five cells), and be separated by thin collagen bands. The hepatocytes in FNH may demonstrate increased levels of glycogen, fatty change, bile stasis, lipofuscin, iron pigment, copper or copper-associated protein, and Mallory bodies.12 Foci of atypical hepatocytes containing larger nuclei and mild hyperchromasia, with or without conspicuous nucleoli, may be seen in some cases.
Another important diagnostic feature is the presence of medium- to large-sized, thick-walled muscular vessels, which often exhibit myointimal myxoid or fibromuscular hyperplastic changes (Figs. 55.6 and 55.7). These vessels are not considered components of a portal tract, because large ducts of similar caliber and portal veins are not associated with them. Portal tracts are absent in FNH except at the periphery of the lesion, although a bile duct of intermediate or large caliber may be found in the central fibrous zone in rare cases.23 The sinusoids may be dilated, and Kupffer cells may be evident. Inflammatory cell infiltrates are relatively common and consist mainly of lymphocytes, although neutrophils and eosinophils may be seen, particularly around bile ductular structures. Rarely, granulomas are identified.
Immunohistochemistry demonstrates intense but patchy staining (i.e., maplike pattern) for glutamine synthetase1,14 (Fig. 55.8), which is distinctly different from the centrizonal hepatocyte staining pattern of normal liver. For FNH-like lesions, portal zones may be seen within the lesion, the ductular reaction may be decreased or lacking, and the central scarlike zone may be absent.
Differential Diagnosis
FNH may resemble HCA or normal liver in small biopsy samples. One of the most important distinguishing features of FNH is the bile ductular reaction (Table 55.4), but it must not be mistaken for the ductular reaction in the inflammatory variant of HCA. Because of the patchiness of the bile ductular reaction, a large-core needle biopsy or a wedge biopsy may be necessary for this feature to be identified. The finding of large blood vessels with abnormal hyperplastic features and usually surrounded by at least a moderate amount of connective tissue may be helpful, because the blood vessels in HCA tend to have a more normal configuration and lack significant perivascular connective tissue stroma.
Table 55.4
Comparison of Hepatocellular Adenoma and Focal Nodular Hyperplasia
| Morphologic Feature | Hepatocellular Adenoma | Focal Nodular Hyperplasia |
| Hepatocytes | Similar in size, slightly larger or smaller than in normal liver; rare tumors show pleomorphism; cytoplasmic glycogen or fat may be seen | Usually normal in size; no significant cytologic abnormalities but possible foci of cellular pleomorphism; glycogen or fat may be seen |
| Bile ductules | None (except in inflammatory HCA) | Present in fibrovascular zone, typically at edges of hepatocytic nodules |
| Vessels or other blood-filled spaces | Large vessels often seen but without surrounding connective tissue zone; small to medium-sized, isolated hepatic arteries; peliosis hepatis and sinusoidal dilation | Abnormal, large, muscular vessels surrounded by connective tissue stroma |
| Connective tissue component | Occasional fibrous septa | Fibrovascular central zone; myxoid or dense collagen; chronic inflammatory infiltrates; possible focal sinusoidal fibrosis |
| Encapsulation | Occasionally occurs, often discontinuous | None |
| Cell plate architecture | 1 to 3 cells wide; regenerative appearance | 1 to 3 cells wide; plates may be compressed; foci of plates > 3 cells wide may be seen |
| Reticulin stain | Normal or slightly decreased; may have acinar-like pattern | Normal staining pattern but can show irregular architecture with wider cell plates and small acinar change |
| Immunohistochemistry | β-Catenin, SAA, CRP staining and lack of LFABP1 staining define variants | GS maplike staining |
| Other features | Patient age: between 10 and 50 yr; typically female; normal serum AFP level and possible increased alkaline phosphatase level, large lesions prone to hemorrhage | Young adults, female > male; normal AFP level; radiographic imaging often demonstrates central fibrous zone |
AFP, α-Fetoprotein CRP, C-reactive protein; LFABP1, liver-type fatty acid binding protein 1; GS, glutamine synthetase; HCA, hepatocellular adenoma; SAA, serum amyloid A.
The use of immunohistochemical stains can help to differentiate FNH from HCA. SAA and CRP typically are diffusely positive in inflammatory HCA but show very limited or no focal staining in FNH. Staining for glutamine synthetase in FNH should be intense and extensive compared with the patchy perivenular staining or lack of staining in HCA. The exception is the β-catenin–mutated variant of HCA, which may show diffuse intense staining of glutamine synthetase.
Similar to HCA, FNH normally stains positively for hepatocellular markers, including the cytokeratin (CK) marker CAM 5.2 and the canalicular marker polyclonal CEA. The reticulin stain typically demonstrates an intact reticulin framework in FNH, as in HCA, but rare foci may also show cell plates three to five cells thick, and care must be taken not to mistake this finding for HCC.28 A copper stain may demonstrate deposits in hepatocytes adjacent to fibrous bands.28 CD34 often is positive in endothelial cells that line cell plates, although to a lesser extent than in many HCAs and HCCs, but in any one case, this marker is not reliable for distinguishing FNH from HCA or HCC.18 However, CD34 may still be useful for demonstrating lesional tissue in the sample. Staining for AFP is typically negative in FNH.
Treatment
Surgical resection is usually unnecessary unless the lesion is pedunculated or very large, in which case there is a risk for torsion and hemorrhage, or for abdominal pain and distress. Excision of FNH is justified if the lesion cannot be differentiated from HCC or HCA with confidence.
Benign and Dysplastic Lesions in the Cirrhotic Liver
A review of the terminology recommended for cytologic changes is necessary to discuss the various types of nodules that occur in cirrhosis. Cirrhotic nodules frequently contain scattered, enlarged hepatocytes with abundant cytoplasm and atypical, enlarged nuclei with a preserved nucleus-to-cytoplasm ratio (Fig. 55.9). This cytologic feature was previously designated large cell dysplasia. However, the International Working Party recommends the term large cell change12 for this finding because the alteration in this typical pattern of scattered cells in cirrhosis is not definitely dysplastic and more likely a degenerative change.29 This type of cellular change is quite prevalent.29
Cirrhotic nodules may contain small hepatocytes with normal, slightly smaller, or slightly larger nuclei and scant cytoplasm, which results in an overall increase in the nucleus-to-cytoplasm ratio (Fig. 55.10). This cytologic feature was previously designated small cell dysplasia, but the International Working Party recommends the term small cell change for the process.12 The consensus is that small cell features in cirrhotic livers may be regenerative rather than dysplastic and may be preneoplastic only in certain instances, such as when the cells are arranged in clusters in a cirrhotic nodule.
Clusters of small cells may be seen in any type of cirrhotic nodule and may be only 1 to 2 mm in diameter, which imparts the appearance of a nodule within a nodule (see Fig. 55.10). This type of change has been referred to as a dysplastic focus, without further classifying it as low or high grade.12 Dysplastic foci have a high prevalence among diseases such as chronic hepatitis B virus (HBV) and chronic hepatitis C virus (HCV) infection, α1-antitrypsin deficiency, and tyrosinemia.12 Dysplastic foci may also contain cells with enlarged nuclei and hyperchromasia and with minimal to severe nuclear atypia. Cytoplasmic fat (i.e., glycogen) often is different from that seen in the surrounding liver. The International Working Party recommends that the term dysplasia be used only for dysplastic foci or for bona fide dysplastic nodules and not for scattered cytologic changes in a cirrhotic liver.
The whole nodule may be abnormally large or dysplastic, and these nodules have been designated as large regenerative nodules and as low and high-grade dysplastic nodules. The dysplastic nodules are thought to be part of the pathogenetic pathway to HCC.30
Macroregenerative Nodules and Low-Grade Dysplastic Nodules
Nomenclature
In cirrhosis, benign nodules larger than typical cirrhotic nodules have been referred to by various names, including large regenerative nodule12 and macroregenerative nodule. Low-grade dysplastic nodules are thought to represent a clonal proliferation of hepatocytes. However, because the gross and microscopic features of large regenerative nodules and low-grade dysplastic nodules are often indistinguishable, the following description applies equally to both lesions.
Many clinicians do not try to distinguish large regenerative nodules from low-grade dysplastic nodules, because clonality studies may be the only valid method for doing so. In clinical practice, these terms are used interchangeably to describe a nodule that is distinct from the surrounding cirrhotic liver but lacks the cytologic or architectural abnormalities characteristic of high-grade dysplastic nodules. I prefer the term macroregenerative nodule for these lesions and reserve the dysplastic label for high-grade lesions.
For similar-appearing nodules in noncirrhotic livers, the International Working Party recommends the term multiacinar regenerative nodules.12 They tend to occur in the setting of Budd-Chiari syndrome or portal vein thrombosis or as a sequela of hepatocyte necrosis with regeneration. These lesions may be similar to FNH and be designated as FNH-like lesions, (see Focal Nodular Hyperplasia). Large regenerative nodules and multiacinar regenerative nodules represent a reactive process rather than a clonal preneoplastic lesion.
Clinical Features
Macroregenerative nodules and low-grade dysplastic nodules occur in the setting of cirrhosis, with only a few exceptions, such as in the setting of chronic liver disease without fully developed cirrhosis.31 They are usually an incidental finding at autopsy or at the time of transplantation, but they may also be identified on radiographic studies. The serum AFP concentration is typically normal or within the low range expected for the underlying chronic liver disease or cirrhosis.
Pathogenesis
These nodules usually are considered benign lesions, but nodules with this histologic appearance have been associated with an increased incidence of HCC.32 Almost no previous studies of macroregenerative nodules have attempted to define the lesions as regenerative or clonal but instead have defined them as lacking features of high-grade dysplastic nodules or HCC on routine histologic examination. The literature may be somewhat contradictory, and it cannot be definitively stated whether regenerative nodules and clonal, low-grade dysplastic nodules have similar risks for HCC. These nodules are typically seen in cirrhosis related to HBV or HCV infection, alcohol consumption, or hemochromatosis, and they are less likely to be seen in primary biliary cirrhosis. The risk factors for development of macroregenerative nodules are similar to those for HCC.
Pathologic Features
Macroregenerative nodules or low-grade dysplastic nodules are larger than typical cirrhotic nodules. The generally accepted lower limit is between 0.8 and 1 cm in diameter, and the higher limit is less than 3 cm in the greatest diameter. These nodules tend to bulge on cut section. The edges of the nodules are usually round and sharply circumscribed, and they may be more deeply bile stained or paler than typical cirrhotic nodules.
Histologically, these nodules resemble cirrhotic nodules. They have an intact reticulin framework similar to that of normal liver, and the cell plates are usually one or two cells thick (Figs. 55.11 and 55.12). The hepatocytes typically have unremarkable cytology, although some focal variation in cell size and scattered large cell change similar to that seen in other cirrhotic nodules may be seen in large regenerative nodules. Low-grade dysplastic nodules are expected to have a more uniform population of hepatocytes because of their clonal nature, but many specific features of this type of clonal nodule have not been definitively established. Findings such as Mallory bodies, bile stasis, clear cell cytoplasmic changes, iron or copper deposits, a slight decrease in cell size,33 and focal or diffuse fatty changes may be seen. Portal tracts are usually seen in the nodule, and bile ductular reaction may be prominent. Fibrous septa that extend into the nodule without a complete triad of duct, vein, and artery may be identified.34
Differential Diagnosis
The size of this nodule is important for differentiating it from typical cirrhotic nodules. Rarely, a nodule with this histologic pattern lacks portal structures, but this does not warrant a diagnosis of adenoma in a cirrhotic liver without one of the risk factors for adenoma. Features that differentiate these nodules from high-grade dysplastic nodules and small, well-differentiated HCCs are outlined in Table 55.5.
Table 55.5
Differentiating Features of Macroregenerative and Dysplastic Nodules and Well-Differentiated Hepatocellular Carcinoma
| Morphologic Feature | Macroregenerative (Large Regenerative) Nodule | Low-Grade Dysplastic Nodule | High-Grade Dysplastic Nodule | Well-Differentiated Hepatocellular Carcinoma |
| Hepatocyte size | Similar to cirrhotic nodules | A uniform population of hepatocytes with normal cytologic features suggesting clonal proliferation | Variable, usually close to normal or slightly smaller | Smaller or larger cells, often in a diffuse pattern |
| Small cell change or nuclear density >2 times normal | Absent or scattered cells | Absent or scattered cells | Occasional small foci but nuclear density <2 times normal; diffuse or prominent; dysplastic focus may have appearance of a nodule within a larger nodule | Small to large zones common; nuclear density >2 times normal |
| Large cell change | Scattered cells may be seen | Absent | Scattered cells may be seen; zones of cells in dysplastic focus | May be seen instead of or in addition to small cell change |
| Cell plates ≥3 cells thick and trabeculae | Absent | Absent | Focal plates >3 cells thick but no trabeculae | Plates >3 cells thick; trabeculae common |
| Reticulin framework | Intact | Intact | Focal loss or decreased reticulin | Extensive loss or highlights abnormal plate architecture; occasionally, reticulin staining is more prominent with thickened bands separating cell plates |
| Increased iron deposits | Sometimes present | Unknown | Sometimes occurs | Typically absent, even in siderotic liver |
| Periphery of nodule | Well circumscribed | Well circumscribed | Some with irregular borders | Infiltrative or irregular borders representing parenchymal or stromal invasion |
| Portal tracts or fibrous tissue zones | Typically seen; focal bile ductular reaction | Usually seen | Normal portal tracts uncommon, usually absent | No intact portal tracts unless entrapped at edge of tumor; fibrous zones may separate cell plates, and tumor may invade stroma; ductular reaction often not seen in adjacent stroma |
| Mitoses | Rare | Rare | Few | Few to common |
Studies of the vascularity of these nodules have shown that they have a large number of arteries unassociated with other components of a normal portal space. They are referred to as unpaired arteries. However, staining for CD34 or CD31, as a marker for sinusoidal capillarization, is usually similar to that seen in cirrhotic nodules; some peripheral staining is normally seen at the edge of the nodules.35,36 The nodules are usually negative for AFP37 and otherwise show a staining pattern similar to that expected in normal liver for cytokeratin and polyclonal CEA.
Treatment
Therapy for macroregenerative nodules varies because most lesions are found incidentally on excision or explantation. For lesions that have not been excised, clinical follow-up for an increase in size or other features that suggest malignant transformation is recommended.
High-Grade Dysplastic Nodules
Clinical Features
High-grade dysplastic nodules,12,34 previously known as borderline nodules,33 almost always occur in cirrhotic livers. The serum AFP level is usually normal or within the range typical of chronic liver disease or cirrhosis. The lesions may enhance on radiographic imaging, but lesions less than 1 cm in diameter tend to fall below the limits of radiographic resolution.
Pathogenesis
High-grade dysplastic nodules, which typically occur in the setting of cirrhosis, are considered a premalignant change in the carcinogenic pathway to HCC. Various pathologic features and molecular features support this theory (see Chapter 44).
Pathologic Features
High-grade dysplastic nodules essentially have the same gross features as large regenerative or low-grade dysplastic nodules, although some may appear less circumscribed or have an irregular border.
Microscopically, when dysplastic changes are observed uniformly throughout a nodule, a designation of high-grade dysplastic nodule is warranted. A nodule containing one or more dysplastic foci is referred to as a dysplastic nodule (see Fig. 55.10). The atypical features of these lesions are not overtly severe enough to be diagnostic of HCC, but they are more atypical than expected in usual cirrhotic nodules. The nodule is often recognized by zones of small cell change (see Fig. 55.10) with an increased nucleus-to-cytoplasm ratio (i.e., increased nuclear density), which is defined as an increased number of hepatocyte nuclei per microscopic field compared with normal liver.33 Large cell change, which is rarely a feature of high-grade dysplastic nodules, may be identified in a discrete zone of atypical cells rather than as enlarged nuclei scattered singly throughout the nodule.
Other common features of high-grade dysplastic nodules include focal zones of cell plates that measure as much as three cells thick, a focal decrease in the reticulin framework, and mild dilation of sinusoids. These nodules may also contain foci of Mallory bodies, fat, clear cell change, cytoplasmic basophilia, rare mitoses, bile, and portal tracts. The nodules may contain iron deposits. High-grade dysplastic lesions tend to lack iron deposits, which are more common in low-grade nodules. The borders of these nodules may be irregular, and focal acini (pseudoglands) may be seen.
Differential Diagnosis
High-grade dysplastic nodules are differentiated from overt HCC by several features (see Table 55.5). Those particularly helpful for diagnosing HCC include the mitotic figures in moderate numbers, trabeculae, cell plates greater than three cells thick, nuclear density more than two times normal, marked reduction in the reticulin framework, numerous unpaired arteries, and absence of portal tracts. High-grade dysplastic nodules are more likely to show an immunostaining pattern similar to that of HCC, such as sinusoidal staining with CD34 and rare positivity with GPC3 (see Hepatocellular Carcinoma and Its Variants).19,38
Treatment
Most authorities recommend excision or ablation of high-grade lesions because they are thought to represent the early stage of a malignant process. Sampling by small-core biopsies may miss the areas of tissue diagnostic of HCC, which may be found focally in high-grade dysplastic nodules.
Hepatocellular Carcinoma and Its Variants
Clinical Features
HCC is the most common primary malignant tumor in the liver. In approximately 85% of cases in the United States, HCC occurs in the setting of cirrhosis.39 The incidence of HCC varies by geographic location, with a low incidence in Europe and North America (2 to 7 cases per 100,000 persons) and a high incidence in eastern Asia and southern Africa (30 cases per 100,000 persons). The incidence of HCC generally increases with age, but the mean age of occurrence depends on the specific geographic location. For example, in North America, the mean age at diagnosis is approximately 60 years, but in Africa, the average age is approximately 35 years. In Taiwan, the mean age of occurrence ranges from 40 to 60 years.40 HCC is three times more common among men than women, and worldwide, it is the fifth most common type of malignancy in men and the eighth most common in women.
The presenting symptoms vary, but many patients are completely asymptomatic or have mild abdominal pain. Other signs of HCC include weight loss, jaundice, ascites, malaise, and fever. Late serious complications of large HCC tumors include rupture with hemorrhage and disease that is metastatic most often to the abdominal cavity or lungs.
Many patients with cirrhosis are diagnosed by imaging or an elevated serum AFP level. Lesions smaller than 1.5 cm in diameter usually do not enhance on radiographic angiography, and HCC may be more echogenic or less echogenic than adjacent normal liver parenchyma. Almost two thirds of patients with large HCC tumors have a high serum AFP level (>1000 ng/mL).39 Tumors smaller than 2 to 3 cm in diameter are unlikely to be associated with an elevated serum AFP level.37 A serum AFP level of less than 500 ng/mL may be seen in many types of liver disorders. Elevation of AFP levels to between 500 to 1000 ng/mL suggests HCC but is not specific. Other types of malignancies, such as some types of tubal gut adenocarcinomas, ovarian tumors, and germ cell tumors, may also have markedly elevated AFP levels.
Pathogenesis
HCC develops during a long period and is probably a multistep process that involves various risk factors (e.g. chronic hepatitis), exposure to certain toxic or viral agents, and genetic alterations (see Chapter 44).41 The major etiologic association is cirrhosis, but HBV or HCV infection is also an independent predisposing factor. Patients with cirrhosis resulting from hemochromatosis or α1-antitrypsin disease have an increased risk of HCC compared with patients with cirrhosis related to other causes (excluding HBV and HCV). Other risk factors include exposure to thorium dioxide (Thorotrast), aflatoxins, and estrogenic steroids.9 Stem or progenitor cells in the liver have the potential to differentiate into hepatocytic and biliary cell types, and they may play a role in the pathogenesis of primary liver tumors, particularly HCC, cholangiocarcinoma, or mixed HCC and cholangiocarcinoma,42,43 but their exact role remains unclear.
Pathologic Features
In the United States, most HCC tumors arise in cirrhotic livers. The liver of a patient with HCC may be more bile stained or paler than a nontumorous liver, and it may have irregular borders or satellite nodules. Rarely, the entire lesion is composed of multiple nodules similar in size to typical cirrhotic nodules (Fig. 55.13). Large vein invasion and a fibrous capsule may be identified, particularly in association with large tumors. Small HCCs (<2 cm in diameter) usually lack vascular invasion, necrosis, and hemorrhage.
The WHO1 has described the four typical histologic patterns of HCC: trabecular, acinar, compact, and scirrhous. The trabecular (platelike) pattern is the most common (Fig. 55.14). In this variant, tumor morphology mimics the cell plate architecture of normal liver but has important differences. The cell plates in trabecular HCC are typically three or more cells thick, whereas the cell plates in normal or regenerative liver are normally only one or two cells thick. As in normal liver, tumor cell plates are lined by endothelial cells, but reticulin staining usually shows that the reticulin framework is absent or markedly decreased or distorted, with irregular or absent staining of the borders of the trabeculae (Fig. 55.15). Tumor cells often have features of a small cell change (see Figs. 55.14 and 55.15). Large cell change may be seen infrequently, except in high-grade tumors. Foci of small and large cell changes often are admixed. Kupffer cells are typically absent in HCC. Occasionally, the tumor cell plates (or trabeculae) may be separated by an increased amount of connective tissue instead of by endothelial cells (Fig. 55.16), and reticulin staining is usually increased in the bands of connective tissue. The thickened cell plates, which are separated by a prominent reticulin framework, often have a linear or ribbon-like arrangement. This pattern has been subclassified as an early form of scirrhous HCC, although the overall amount of fibrous tissue may not be as high as previously described.
The acinar (pseudoglandular) pattern of HCC is less common than the trabecular pattern. This variant is defined by glandlike spaces (i.e., acini) that are lined by hepatocytic tumor cells (Fig. 55.17). The acinar structures are formed by dilation or expansion of bile canaliculi, and they often contain bile or proteinaceous material. Less frequently, the spaces develop as a result of central necrosis of trabeculae and contain protein, cellular debris, or macrophages. The formation of glandlike spaces can lead to a misdiagnosis of adenocarcinoma. The acinar pattern is frequently admixed as a minor component with the trabecular pattern (see Fig. 55.15).
The compact (solid) pattern of HCC is a relatively uncommon variant characterized by dense aggregates of tumor cells that seem to lack endothelial cell–lined trabeculae or cell plates (Fig. 55.18), and it is more common in poorly differentiated HCC. However, careful examination with endothelial cell markers often reveals compressed trabeculae. Loss of the reticulin framework is typically seen in solid and crowded cellular zones.
The scirrhous pattern contains prominent, focal or diffuse areas of fibrosis and may be associated with any of the patterns previously described (Fig. 55.19). Differentiation of scirrhous HCC from fibrolamellar HCC (see Fibrolamellar Variant of Hepatocellular Carcinoma) is based on identification of the characteristic cytologic features of the latter and on the different clinical settings in which these two tumors occur. The term sclerosing hepatic carcinoma has been used for some of the HCCs and cholangiocarcinomas associated with hypercalcemia, but this form is not recognized as a distinct variant.44
In all of these patterns, the cytologic features of HCC tend to resemble those of normal hepatocytes, but the degree of nuclear atypia varies, ranging from near normal to markedly abnormal (i.e., angular nuclei with clumped chromatin). The tumor cells often maintain their polygonal shape and have round vesicular nuclei and prominent nucleoli that exhibit features typical of hepatocytic differentiation. Intranuclear vacuoles (composed of cytoplasmic invaginations) and glycogenation of nuclei (another feature seen in normal liver) are fairly common in HCC tumors (Fig. 55.20). Small cell change is probably the most common atypical cytologic change, but a large cell change and giant or pleomorphic cells may be seen focally or diffusely (see Fig. 55.20). The amount of cytoplasm may vary, and it is often slightly more basophilic than in normal hepatocytes. The cytoplasm may have a granular appearance, or it may be exceptionally oxyphilic because of a large number of mitochondria. Cytoplasmic inclusions (e.g., Mallory bodies, globular acidophilic bodies) composed of proteins (i.e., albumin, fibrinogen, α1-antitrypsin, or ferritin) may be seen (see Fig. 55.20).
Fat (Fig. 55.21), glycogen, or possibly water may be prominent in HCCs, providing the cells with a clear appearance. This has been described as the clear cell variant of HCC. If the entire tumor shows this type of clear cell change and it occurs in a noncirrhotic liver, it may be difficult to differentiate HCC from other types of clear cell tumors, such as metastatic renal cell carcinoma (see Differential Diagnosis). Other cytoplasmic changes seen much less frequently include pale bodies, which are round to oval, lightly eosinophilic or clear cytoplasmic structures most frequently seen in the fibrolamellar variant of HCC; ground-glass cells containing hepatitis B surface antigen, which is found in some patients with HBV infection45; and dark brown to black pigment similar to that seen in the Dubin-Johnson syndrome. Rare forms of HCC that show a prominent spindle cell component or diffuse small cells (i.e., small cell type) have been described.
Histologic Grading of Hepatocellular Carcinoma
Grading of HCC is based on the system developed by Edmondson and Steiner in 1954.46 These investigators originally defined four grades that were distinguished by proportional increases in the nucleus-to-cytoplasm ratio, variability in nuclear shape, hyperchromasia, and loss of cell plate architecture from low- to high-grade tumors. This grading system is still used with some minor modifications,6 but descriptive rather than numeric designations are used.1 Methods that use nucleus-to-cytoplasm ratios and proliferative rates are not typically applied.
Some of the Edmondson-Steiner well-differentiated (grade 1) tumors with minimal cytologic atypia and architectural distortion were recognized as malignant only by their association with an admixture of high-grade HCC or by the finding of metastatic lesions.39,46 With the current criteria established by the International Working Party6 and the International Consensus Group for Hepatocellular Neoplasia,30 the stricter definition of grade 1 lesions may help to reclassify some of these lesions as early HCC or as low- or high-grade dysplastic nodules. Ideally, a true grade 1 HCC exhibits definitive architectural features of malignancy or invasion (see Table 55.5), even though it shows little or no cytologic atypia.
Grade 2 tumors are well differentiated. They typically have a trabecular pattern, but they have larger nuclei than grade 1 tumors. Grade 2 lesions may also contain acinar structures and bile.
Grade 3 tumors are moderately differentiated, and they have greater cytologic and architectural variability than grade 2 lesions. Multinucleated (giant) cells are often seen focally, and unlike grade 2 lesions, they usually do not contain bile. When identified, trabeculae typically are wider or have a more varied structure than in grade 2 tumors.
Grade 4 tumors are poorly differentiated or anaplastic tumors in which classification of the lesion as HCC is difficult without knowledge of other clinical or serologic parameters, such as the presence or absence of cirrhosis or an increase in serum level of AFP. Grade 4 lesions include spindle cell and small cell HCC tumors.
An alternative three-grade system is also used. With the three-tier system, grade 1 represents well-differentiated lesions (combined grades 1 and 2 from the previously described system), grade 2 represents moderately differentiated lesions, and grade 3 comprises poorly differentiated and anaplastic lesions. Regardless of which grading system is used, vascular invasion and poor differentiation are considered independent risk factors for a poor prognosis. The current WHO system adapts these criteria and recommends the terminology of well, moderately, and poorly differentiated and undifferentiated for grades of HCC.1
Early or Small Hepatocellular Carcinoma
Small HCC, defined as those less than 2 cm in diameter, are typically well-differentiated tumors with histologic features that often include fat, small acinar changes, intratumoral portal zones, thin cell plates (less than three cells thick), and unpaired arteries.1,30 Another helpful diagnostic marker for possible early HCC is the relative lack of ductular reaction surrounding the edges of the lesions.47 Molecular aspects of transformation to early HCC and concepts of progression are discussed further in Chapter 42. These lesions can be so well differentiated that the primary means of making the diagnosis of HCC may depend on identifying tumor invasion into adjacent stroma or parenchyma.
Rare Variants of Hepatocellular Carcinoma
Variants of HCC that have been selected by the WHO1 for special consideration include the types known as lymphoepithelioma-like carcinoma and sarcomatoid HCC.
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