Diagnostic utility of the HepPar1 antibody to differentiate hepatocellular carcinoma from metastatic carcinoma in fine-needle aspiration samples.

The cytopathologic distinction between hepatocellular carcinoma (HCC) and metastatic carcinoma (MC) in the liver can be problematic, especially in patients with poorly differentiated HCC, in whom a trabecular pattern, bile production, and Mallory bodies may not be apparent on small fine-needle aspiration (FNA) samples. HepPar1 (OCH1E5) is a monoclonal antibody specifically developed to react with hepatocytes. It rarely reacts with bile duct and nonparenchymal liver cells. FNA samples (cell blocks) from 75 liver tumors were selected. These included 50 moderate to poorly differentiated HCC cases, 5 cholangiocarcinoma (CC) cases, and 20 MC cases (4 from the breast, 4 from the stomach, 4 from the pancreas, and 8 from the colon). Immunohistochemical staining for HepPar1 was performed to differentiate HCC from MC. The HepPar1 antibody was positive in 50 of 50 HCC cases (100%). The positivity was cytoplasmic, diffuse, and granular. All 5 cases of CC were found to be negative (0%). Although focal positivity within tumor cells was noted in one case, cytologically these were entrapped normal hepatocytes between the tumor cells. In addition, 3 of 20 MC cases (15%) also were positive for HepPar1. All three cases originated from gastric primary tumors and exhibited diffuse, granular cytoplasmic staining. The results of the current study demonstrate that HepPar1 is an effective marker with which to differentiate between HCC and CC and/or MC. HepPar1 was found to demonstrate 100% positivity in HCC cases, compared with 0% and 15% positivity, respectively, in CC and MC cases. In addition, HepPar1 is extremely helpful in limited tissue samples from FNA. Although 15% of the MC cases in the current study were found to be positive, with the help of clinical correlation and other immunohistochemical stains a definite diagnosis could be rendered. Potential pitfalls include residual benign hepatocyte staining within a non-HCC malignancy, as was observed in one of the CC cases in the current study.