Pathology of small hepatocellular carcinoma. A proposal for a new gross classification

Review of 61 surgically resected small hepatocellular carcinomas (HCC) less than or equal to 3 cm in diameter yielded a simple gross classification system of five types based on tumor shape, which is highly correlated with microscopic and clinical features, including prognosis. Type 1 (single nodular type) tumors (n = 13) are expansile, roughly spheric, and often encapsulated. In Type 2 tumors (single nodular type with extranodular growth) (n = 21), replacing growth is often seen in the area of extranodular growth. Type 3 tumors (contiguous multinodular type) (n = 19) consist of small nodules growing in contiguity, often with replacing growth at the periphery. Type 4 (poorly demarcated nodular type) is a rare tumor showing infiltrating growth at its border. The authors define early HCC (n = 5) as the presence of tumor without destruction of the underlying liver structure. The lesions experienced are tiny (≤1.2 cm) and well differentiated. Poorly differentiated histologic characteristics and elevated alpha fetoprotein are more common in Types 2 and 3 than in Type 1. Type 1 has the highest rates of positive serum hepatitis B surface antigen and liver cirrhosis; portal vein tumor thrombus (PT) and/or intrahepatic metastasis (IM) is rare (7.7%), and the effect of transcatheter arterial embolization (TAE) is remarkable. This contrasts with Type 2, which has a high rate of PT and/or IM (71.4%) and multiple local recurrences (40%), and with Type 3, which shows a poor response to TAE.