Immunohistological evaluation of single small hepatocellular carcinoma with negative staining of monoclonal antibody Hepatocyte Paraffin 1

BACKGROUND AND OBJECTIVES: The sensitivity and specificity of the monoclonal antibody Hepatocyte Paraffin 1 (Hep Par 1) for hepatocellular carcinoma (HCC) are very high, and the usefulness for differential diagnosis of hepatic tumors has been reported. However, there are some cases of HCC with negative staining for Hep Par 1. We examined the histopathological features of HCC with negative staining for Hep Par 1. METHODS: We examined 69 samples of single nodular HCC less than 2 cm in greatest dimension, resected from 1985 to 1994 in our hospital, with immunohistological staining for Hep Par 1, cytokeratin 19 (CK 19), MUC-1 glycoprotein (MUC-1), and epithelial membrane antigen (EMA). RESULTS: Hep Par 1 staining was positive in 64 cases (93%) and negative in 5 cases (7%). With regard to the histological structure, 3 of the 5 negative cases were scirrhous HCC. With regard to the grade of histological differentiation, 2 cases were poorly differentiated HCC, 3 cases were moderately differentiated HCC, and no well-differentiated HCC was found in the negative cases. CK 19, MUC-1, and EMA staining were negative in all cases. CONCLUSIONS: It is necessary to recognize the existence of Hep Par 1 negative HCC, in particular scirrhous HCC. This may be due to a different mechanism in the earlier stage of hepatocarcinogenesis.