In tumors exhibiting adenocarcinoma morphology, markers such as CK7, CK19, CK20, CDX2, TTF1, GATA-3, PAX8, TRSP-1, GCDFP-15, Mammaglobin, NKX3.1, and PSAP are utilized for distinguishing primary cholangiocarcinoma from metastatic adenocarcinomas and for identifying the primary origin of metastatic tumors. The gene discussed is PAX8; the disease is metastatic neoplasm.