Diagnostic value of hepatocyte paraffin 1 antibody to discriminate hepatocellular carcinoma from metastatic carcinoma in fine-needle aspiration biopsies of the liver.

Diagnosing liver tumors by fine-needle aspiration biopsy is safe and accurate. However, there are cases that prove diagnostically difficult. Traditionally, immunostains for alpha-fetoprotein and polyclonal carcinoembryonic antigen have been used to distinguish adenocarcinomas from hepatocellular carcinomas (HCCs). In poorly differentiated tumors, these immunostains have limitations in both sensitivity and specificity. An hepatocyte-specific immunostain has been described in the surgical pathology literature. To the authors' knowledge, this hepatocyte antibody has not been studied in liver fine-needle aspiration biopsies. The authors examined the Hepatocyte Paraffin 1 (HP1) antibody for its diagnostic utility in this cytologic setting. Cell-block material from 40 cases of HCC and 53 cases of metastatic adenocarcinoma were studied. Slides were stained for HP1 by the avidin-biotin complex method following antigen retrieval. The percentage of malignant cells that exhibited coarse granular staining in the cytoplasm was estimated for all cases of HCC, poorly differentiated HCC, and metastatic adenocarcinoma. HP1 was expressed in 83% of all HCCs but in only 56% of poorly differentiated HCCs. Only 2 of 53 (4%) of metastatic tumors expressed HP1. The overall sensitivity of HP1 was 79% and its specificity was 96%. HP1 was found to be a specific immunostain that may prove helpful in diagnosing all but the most undifferentiated liver tumors biopsied by fine-needle aspiration.