Intermediate trophoblast in germ cell neoplasms.

One-hundred-twenty-four germ cell tumors and 11 gestational choriocarcinomas were assessed immunohistochemically for the presence of the following placental markers: human chorionic gonadotrophin, human placental lactogen, and pregnancy-specific beta-1 glycoprotein, and for the expression of cytokeratin. A total of 40 cases contained syncytial trophoblastic cells, large mononuclear cells, or both. These cases included all gestational choriocarcinomas and choriocarcinomatous foci in 11 mixed germ cell tumors, 14 embryonal carcinomas, and four seminomas. Syncytial trophoblastic cells reactive for cytokeratin were identified in all choriocarcinomas, 12 embryonal carcinomas, and two seminomas. Human placental lactogen-reactive syncytial trophoblastic cells were observed in nine gestational choriocarcinomas, 10 choriocarcinomatous foci in mixed germ cell tumors, four embryonal carcinomas, and one seminoma. Pregnancy-specific beta-1 glycoprotein-reactive syncytial trophoblastic cells were seen in 10 gestational choriocarcinomas, all choriocarcinomatous foci in mixed germ cell tumors, 11 embryonal carcinomas, and one seminoma. Cytotrophoblasts, as expected, were identified only in choriocarcinomas. Cytokeratin-reactive cytotrophoblast was seen in all gestational choriocarcinomas and 10 choriocarcinomatous foci in mixed germ cell tumors. Human chorionic gonadotrophin-reactive cytotrophoblast was observed in two gestational choriocarcinomas and three choriocarcinomatous foci in mixed germ cell tumors. Cytotrophoblast was uniformly nonreactive for human placental lactogen and pregnancy-specific beta-1 glycoprotein. Cytokeratin-reactive large mononuclear cells were observed in 10 gestational choriocarcinomas, all choriocarcinomatous foci in mixed germ cell tumors, five embryonal carcinomas, and three seminomas. Human placental lactogen-reactive large mononuclear cells were identified in nine gestational choriocarcinomas, seven choriocarcinomatous foci in mixed germ cell tumors, one embryonal carcinoma, and one seminoma. Pregnancy-specific beta-1 glycoprotein-reactive large mononuclear cells were present in 10 gestational choriocarcinomas, 10 choriocarcinomatous foci in mixed germ cell tumors, two embryonal carcinomas, and two seminomas. Because of morphologic and immunohistochemical similarities of large mononuclear cells with intermediate trophoblast of the normal placenta and gestational trophoblastic neoplasms, we propose that the large mononuclear cells in gonadal and extragonadal germ cell neoplasms are equivalent to the intermediate trophoblast.