Answer: Hepatocellular carcinoma, fibrolamellar type

Histology: The tumor consists of cells with abundant polygonal shape and abundant eosinophilic cytoplasm. The nuclei are round to oval with prominent nucleoli. The tumor grows in nests separated by a prominent fibro-hyaline stroma.

Discussion: The fibrolamellar variant of hepatocellular carcinoma is seen predominantly in young patients without cirrhosis. Patient age ranges from 20 to 40 years. Almost half of the hepatocellular carcinomas seen in patients younger than 35 years old are of this type. Grossly, these tumors are well circumscribed and show scarring. Histologically, tumor cells are polygonal and eosinophilic. The most characteristic microscopic feature is the fibrosis that is arranged in a lamellar fashion around the neoplastic cells.

The differential diagnosis mainly includes usual type hepatocellular carcinoma, cholangiocarcinoma and focal nodular hyperplasia. Focal nodular hyperplasia does not have a capsule. It contains large thick vessels, a central scar, and cytologically benign cells. Bile ducts are also seen in focal nodular hyperplasia. The usual type of hepatocellular carcinoma lacks the characteristic lamellar fibrosis of the fibrolamellar type. Cholangiocarcinomas show glandular differentiation.

Immunohistochemistry may be helpful in distinguishing among these lesions. Hepatocellular carcinomas express low molecular weight cytokeratins. In contrast, cholangiocarcinomas express both low and high molecular weight cytokeratins. Polyclonal CEA is usually positive in a cannulicular pattern in hepatocellular carcinoma. In contrast, cholangiocarcinomas show cytoplasmic and luminal staining.

The fibrolamellar variant of hepatocellular carcinoma has a better prognosis compared to usual type hepatocellular carcinoma, with about 60% survival at 5 years and a 50% cure rate.