The use of cytokeratin 7 and EMA in differentiating ovarian yolk sac tumors from endometrioid and clear cell carcinomas.

Yolk sac tumors (YSTs) have a variety of morphologic patterns, some of which can resemble either endometrioid adenocarcinoma (EAC) or clear cell carcinoma (CCC). Immunohistochemical staining for alpha-fetoprotein (AFP) is usually only focal and thus is not always helpful in the diagnosis of YST, and pancytokeratin (CK) is expressed by all three tumors. We studied a battery of immunohistochemical markers with specific attention to the utility of cytokeratin 7 (CK7) in differentiating YST from EAC and CCC.