Inhibin is not an immunohistochemical marker for hepatocellular carcinoma - An example of the potential pitfall in diagnostic immunohistochemistry caused by endogenous biotin

Inhibin is a heterodimeric glycoprotein originally detected in gonadal tiss ues. One report described inhibin immunopositivity in 17 of 19 hepatocellul ar carcinomas (HCCs) and the hepatocytes of the surrounding nonneoplastic p arenchyma. The reported immunohistochemical method, which used avidin-bioti n complex, did not describe blocking endogenous biotin. Since liver tissue may contain high levels of biotin, endogenous biotin may result in false-po sitive immunostaining. We wondered whether this reported immunopositivity r epresented a false-positive result due to unblocked endogenous biotin. By u sing a similar antigen retrieval technique and the same specificity, titer; and clonal source of primary antibody as the aforementioned study, we perf ormed immunostaining for inhibin with and without an endogenous biotin bloc king step on 23 cases of HCC and the surrounding cirrhotic liver: In all ca ses, the HCC and the hepatocytes in the cirrhotic nodules were negative for inhibin when the endogenous biotin blocking step was used. When the blocki ng step was omitted, apparent immunostaining was noted in 20 of 23 HCCs and in the hepatocytes in all cases. Accordingly, HCC and the hepatocytes of t he surrounding cirrhotic liver are immunohistochemically negative for inhib in. The previously reported immunopositivity of HCC and nontumoral hepatocy tes for inhibin represents a false-positive result cine to endogenous bioti n.