Cytokeratin 7, inhibin, and p63 in testicular germ cell tumor: superior markers of choriocarcinoma compared to β-human chorionic gonadotropin.

Choriocarcinoma can be difficult to differentiate from other subtypes of testicular germ cell tumor and can occur unexpectedly in a distant, late metastasis. The aim of this investigation was to identify a marker superior to β-human chorionic gonadotropin (β-hCG) for choriocarcinoma. Sixty-two primary and metastatic testicular germ cell tumors (27 choriocarcinomas, 19 yolk sac tumors, 29 embryonal carcinomas, 28 seminomas, 22 teratomas, 3 epithelioid trophoblastic tumors [ETTs]) were analyzed for immunohistochemical expression of cytokeratin 7 (CK7), inhibin, p63, and β-hCG. All choriocarcinomas and ETTs were strongly positive for CK7, whereas seminomas were negative and 52% of embryonal carcinomas had weak reactivity. Eighty-four percent of yolk sac tumors and 59% of teratomas were CK7 positive. Eighty-nine percent of choriocarcinomas and 100% of ETTs were positive for inhibin, with reactivity highlighting syncytiotrophoblasts, whereas seminomas, embryonal carcinomas, yolk sac tumors, and teratomas were negative. Eighty-five percent of choriocarcinomas expressed p63, with staining mostly in mononucleated trophoblasts, whereas seminomas, embryonal carcinomas, and yolk sac tumors were negative. Teratomas expressed p63 in 32% of cases. β-hCG was reactive in 96% of choriocarcinomas, 33% of ETTs, 46% of seminomas, 54% of embryonal carcinomas, 47% of yolk sac tumors, and 32% of teratomas. β-hCG staining within other subtypes was more likely if choriocarcinoma was present elsewhere in the tumor (P = .0002). CK7 is a highly sensitive marker for choriocarcinoma and differentiates choriocarcinoma from seminoma and embryonal carcinoma. Inhibin and p63 are sensitive and specific for choriocarcinoma versus seminoma, embryonal carcinoma, and yolk sac tumor. To identify choriocarcinoma, CK7, inhibin, and p63 are superior to β-hCG.