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Distinguishing hepatocellular carcinoma (HCC) from metastatic adenocarcinoma (MA) and cholangiocarcinoma (CC) can, at times, be difficult and sometimes requires immunohistochemical analysis. Recently, MOC31, an antibody directed against a cell surface glycoprotein, has been shown to be useful in separating HCC from both MA and CC; however, no study has compared MOC31 and other frequently used immunostains. We compare MOC31 with other commonly used immunostains for HCC, MA, and CC. Formalin-fixed, paraffin-embedded tissue sections from 57 previously characterized hepatic neoplasms (13 HCC, 14 CC, 3 combined HCC-CC, and 27 MA) were immunostained with antibodies directed against MOC31, cytokeratin (CK) 7, CK20, ␣-fetoprotein (AFP), polyclonal carcinoembryonic antigen, Ber-EP4, and Factor XIII-A. Two pathologists reviewed slides, and positivity was defined as more than 1% of cells staining with the appropriate pattern. Positive MOC31 immunostaining was seen in 0 of 13 HCC, 13 of 14 CC, 3 of 3 HCC-CC, and 27 of 27 MA; the staining was strong and diffuse. CK20 reactivity was observed in 0 of 13 HCC, 2 of 14 CC, 0 of 3 HCC-CC, and 12 of 27 MA; CK7 immunostained 4 of 13 HCC, 13 of 14 CC, 3 of 3 HCC-CC, and 15 of 27 MA; AFP was detected in 4 of 13 HCC and 2 of 3 HCC-CC, whereas all CC and MA were negative; polyclonal carcinoembryonic antigen showed immunoreactivity in 12 of 13 HCC and 3 of 3 HCC-CC in a canalicular pattern, whereas diffuse positivity was identified in 13 of 14 CC and 26 of 27 MA; Ber-EP4 immunostained 1 of 13 HCC, 14 of 14 CC, 2 of 3 HCC-CC, and 26 of 27 MA; and Factor XIII-A was negative in all HCC, CC, and MA. MOC31 expression distinguished HCC from adenocarcinoma in 56 of 57 cases. AFP was specific for HCC but was not sensitive. CK7 and CK20 have limited utility in distinguishing HCC from CC or MA, and Factor XIII-A is not useful. Ber-EP4 staining was similar to MOC31, but one HCC did stain with Ber-EP4. Polyclonal CEA yields similar numerical results as MOC31, but the focal nature of the staining and occasional difficulty in evaluating the pattern can make interpretation problematic. We conclude that MOC31 should be a component of the immunohistochemical panel to distinguish HCC from CC and MA.

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