Chromophobe hepatocellular carcinoma with abrupt anaplasia: a proposal for a new subtype of hepatocellular carcinoma with unique morphological and molecular features

Abstract

Hepatocellular carcinomas exhibit heterogeneous morphologies by routine light microscopy. Although some morphologies represent insignificant variations in growth patterns, others may represent unrecognized subtypes of hepatocellular carcinoma. Identification of these subtypes could lead to separation of hepatocellular carcinomas into discrete groups with unique underlying genetic changes, prognosis, or therapeutic responses. In order to identify potential subtypes, two pathologists independently screened a cohort of 219 unselected hepatocellular carcinoma resection specimens and divided cases into potential subtypes. One of these promising candidate subtypes was further evaluated using histological and molecular techniques. This subtype was characterized by a unique and consistent set of histological features: smooth chromophobic cytoplasm, abrupt focal nuclear anaplasia (small clusters of tumor cells with marked nuclear anaplasia in a background of tumor cells with bland nuclear cytology), and scattered microscopic pseudocysts--we designate this variant as 'chromophobe hepatocellular carcinoma with abrupt anaplasia'. Thirteen cases were identified (6% of all hepatocellular carcinomas), including 6 men and 7 women with an average age of 61 years. Six cases occurred in cirrhotic livers. Serum AFP was elevated in 6 out of 10 cases. There were a variety of underlying liver diseases, but cases were enrichment for chronic hepatitis B, P=0.006. Interestingly, at the molecular level, this variant was strongly associated with the alternative lengthening of telomere (ALT) phenotype by telomere FISH. ALT is a telomerase-independent mechanism of telomere maintenance and is found in approximately 8% of unselected hepatocellular carcinomas. In contrast, 11/12 (92%) of the cases of chromophobe hepatocellular carcinoma with abrupt anaplasia were ALT-positive. In summary, we propose that chromophobe hepatocellular carcinoma with abrupt anaplasia represents a new subtype of hepatocellular carcinoma with unique morphological and molecular features.

Figure 1

Chromophobe hepatocellular carcinomas with abrupt anaplasia. Two separate cases are illustrated, with the first case in the left column of panels and the second in the right column of panels. Pseudocysts are evident in both cases (a, b; H&E, original magnification ×40). The cytoplasm of the tumor cells have a ‘chromophobe appearance’ where the staining qualities of the tumor cytoplasm are not as deep as seen in typical hepatocellular carcinomas (c, d; H&E, original magnification ×100). The cytoplasm can be either slightly eosinophilic (c) or basophilic (d). The nuclei of most tumor cells are small and round with small inconspicuous nucleoli. However, cells in small irregularly distributed clusters show marked nuclear anaplasia (e, f; H&E, original magnification ×160).

Figure 2

Mimics of chromophobe hepatocellular carcinomas with abrupt anaplasia. Pseudocysts are a regular feature of chromophobe hepatocellular carcinomas with abrupt anaplasia, but most cases of hepatocellular carcinoma with pseudocysts will not be chromophobe hepatocellular carcinomas with abrupt anaplasia. (a) A hepatocellular carcinoma with pseudocysts that is not a chromophobe hepatocellular carcinoma with abrupt anaplasia (H&E, original magnification ×64). (b) A hepatocellular carcinoma with cytoplasmic findings that somewhat mimic the chromophobe cytoplasm of chromophobe hepatocellular carcinomas with abrupt anaplasia, but this tumor lacks pseudocysts, sudden anaplasia, and has prominent nucleoli, all features inconsistent with chromophobe hepatocellular carcinoma with abrupt anaplasia (H&E, original magnification ×160). (c) A clear cell hepatocellular carcinoma with areas of marked anaplasia. This morphological pattern can be a strong mimic of chromophobe hepatocellular carcinomas with abrupt anaplasia, but the nuclear changes in most clear cell hepatocellular carcinoma (irregular vesiculated nuclei with prominent nucleoli) are sufficient to distinguish this mimic from chromophobe hepatocellular carcinomas with abrupt anaplasia (H&E, original magnification ×160).

Figure 3

Telomere FISH. Telomere-specific FISH demonstrating ALT-positive and ALT-negative tumors. (a) Representative example of a chromophobe hepatocellular carcinoma with abrupt anaplasia demonstrating the ALT phenotype. The arrows indicate the distinctive large, ultrabright, intranuclear foci of telomere FISH signals that mark the ALT-associated telomeric foci. (b) Representative example of an ALT-negative hepatocellular carcinoma with typical morphology. This tumor lacks the morphology of chromophobe hepatocellular carcinoma with abrupt anaplasia. The asterisks indicate robust telomere signals present in the tumor cells. Original magnification ×400. Because the telomere signals in the ALT-positive case quickly become saturated, the cy3 exposure time in a was 200 ms, whereas in b, it was 600 ms.