Canalicular immunostaining of aminopeptidase N (CD13) as a diagnostic marker for hepatocellular carcinoma

Background: Aminopeptidase N (CD13) is expressed in normal and neoplastic liver tissue, where it exhibits a characteristic canalicular pattern (CD13 ^can), similar to that seen for CD10 and when antibodies crossreact with biliary glycoprotein I (p-CEA). Aim: To compare the putative diagnostic use of CD13^can in differentiating between hepatocellular (HCC) and non-hepatocellular carcinomas metastatic to the liver (non-HCC). Methods: A retrospective study comparing 53 HCC specimens with 32 non-HCC specimens. Immunostaining was performed with HepPar1 and antibodies directed against CD10, CD13, p-CEA, and a fetoprotein (AFP). Results: In the HCC group, a canalicular staining pattern was found for CD13, p-CEA, and CD10 in 51, 43, and 33 specimens, respectively. HepPar1 was positive in 29 and AFP in 17 HCC specimens. In the non-HCC group, canalicular immunostaining for CD10 and p-CEA was confined to non-neoplastic liver tissue. One poorly differentiated cholangiocarcinoma showed apical expression of CD13, resembling to some extent CD13^can. Sensitivity and specificity were 96.2% and 97.0%, respectively, for CD13can, 81.1% and 100% for p-CEA^can, 62.3% and 100%, for CD10^can, 54.7% and 99.9% for HepPar1, and 32.1% and 100% for AFP. Conclusions: These results show that CD13^can is more sensitive in differentiating between HCC and non-HCC than CD10^can, p-CEA^can, HepPar1, and AFP.