α-Fetoprotein-producing gastric carcinoma and combined hepatocellular and cholangiocarcinoma show similar morphology but different histogenesis with respect to SALL4 expression.

α-Fetoprotein is expressed in hepatocellular carcinoma, yolk sac tumor, and some gastric carcinomas. The α-fetoprotein-producing gastric carcinoma composed of hepatoid and common adenocarcinoma shows morphological similarities to combined hepatocellular and cholangiocarcinoma. In this study, the expression of putative hepatic stem/progenitor markers (EpCAM, OV-6, DLK-1, and NCAM/CD56), hepatocyte markers (HepParI, α-fetoprotein, glypican 3), and the germ cell marker SALL4 was examined in α-fetoprotein-producing gastric carcinoma (20 cases) and combined hepatocellular and cholangiocarcinoma (20 cases) for evaluation of pathologic differentiation and also the histogenesis of both tumors. The SALL4 protein was expressed in 95% of α-fetoprotein-producing gastric carcinoma, including the hepatoid component (hepatoid gastric carcinoma), but was absent in combined hepatocellular and cholangiocarcinoma. Glypican 3 and α-fetoprotein were detected in all hepatoid-type α-fetoprotein-producing gastric carcinoma but variably in combined hepatocellular and cholangiocarcinoma. NCAM/CD56 was expressed focally in combined hepatocellular and cholangiocarcinoma but was rare in hepatoid gastric carcinoma. EpCAM, DLK-1, and OV6 were variably expressed in hepatoid gastric carcinoma and combined hepatocellular and cholangiocarcinoma. SALL4 was a useful differential marker for combined hepatocellular and cholangiocarcinoma and hepatoid gastric carcinoma. The histogenesis of hepatoid gastric carcinoma expressing SALL4 seems to reflect fetal gut differentiation or involve the germ cell lineage and may be different from that of combined hepatocellular and cholangiocarcinoma involving the hepatic stem cell or progenitor cell lineages. In conclusion, hepatoid gastric carcinoma and combined hepatocellular and cholangiocarcinoma shared morphologies, whereas the distinction of hepatoid gastric carcinoma from combined hepatocellular and cholangiocarcinoma is possible by immunostaining for SALL4. These 2 tumors seem to differ in their histogenesis with respect to SALL4 expression.1.