Immunohistochemical studies of trophoblastic tumors.

Although intermediate trophoblastic tumors (ITTs) are rare forms of trophoblastic neoplasia, their recognition is important as they require distinct therapeutic approaches. We have noted mixed trophoblastic tumors, with a combination of placental site trophoblastic tumor and epithelioid trophoblastic tumor patterns within the same case, and more frequently a combination of ITT with choriocarcinoma, which can create difficulty in the classification of these tumors. The distinction of the ITTs from choriocarcinoma is important because ITTs do not respond as well to chemotherapy as choriocarcinoma. In addition, ITTs can be confused with a variety of malignant neoplasms, the most common of which is poorly differentiated carcinoma of the cervix. Immunohistochemistry is one means of identifying trophoblastic tumors and of distinguishing them from other entities. We investigated the immunophenotype of 15 ITTs, 11 choriocarcinomas, and 10 primary cervical carcinomas using a panel of human placental lactogen, p63, CK5/6, CK18, human chorionic gonadotropin (hCG), human leukocyte antigen (HLAG), Mel-CAM, (CD146) carcinoembryonic antigen, CD10, inhibin, p16, and pan-keratin. CD10 was positive in all the cases of ITT and choriocarcinoma. HLA-G expression was present in 93% of ITTs and all choriocarcinoma cases. hCG was positive in 87% of ITTs and 100% of choriocarcinomas. We concluded that a panel consisting of HLA-G, CD10, and hCG can be very helpful in the identification of the ITTs. Adding CK5/6 to these markers can help to differentiate ITT from primary cervical carcinoma. However, the distinction of ITTs from choriocarcinoma cannot be accomplished on immunohistochemical studies, as they have similar immunophenotypes.