Keratin 7 is a marker for a subset of trophoblastic cells in human germ cell tumors

Human testicular germ cell tumors were studied immunohistochemically with the monoclonal antibody to the 54-kd keratin polypeptide (keratin 7) to determine whether this antibody could be used selectively to identify trophoblastic cells. The antibody reacted with the intermediate filaments in the cytoplasm of some cells in choriocarcinoma cell lines, and in trophoblastic cells in mixed germ cell tumors and a seminoma. It did not react with classic seminoma cells, embryonal carcinoma, yolk sac carcinoma, or somatic tissues of mixed germ cell tumors. On the basis of these data we conclude that monoclonal antibody to keratin 7 is a marker for a subset of trophoblastic cells in human germ cell tumors.