Immunocytochemical Localization of Placental Lactogen and Chorionic Gonadotropin in the Normal Placenta and Trophoblastic Tumors, with Emphasis on Intermediate Trophoblast and the Placental Site Trophoblastic Tumor

This report presents preliminary observations on the immunocytochemical localization of human chorionic gonadotropin (hCG) and human placental lactogen (hPL) in placental site trophoblastic tumors, hydatidiform moles, and choriocarcinomas and compares the findings with those of a similar immunocytochemical analysis of the placenta at various stages of development. In addition to cytotrophoblast (CT) and syncytiotrophoblast (ST), a third form of trophoblast designated "intermediate trophoblast" (IT) is present during normal pregnancy and in trophoblastic disease. Intermediate trophoblastic cells are mononucleate, larger than CT, and contain more abundant eosinophilic cytoplasm, resulting in a partial resemblance to ST. Intermediate trophoblast has distinctive immunocytochemical features that distinguish it from CT and ST. The localization of hPL and hCG in both IT and ST varies with the age of the placenta, with the type of trophoblastic neoplasm, and from one specimen to another within each category of tumor. Syncytiotrophoblast may contain both hormones in large amounts, whereas IT contains hPL predominantly and hCG focally. Cytotrophoblast is devoid of hCG and hPL except in choriocarcinoma, which may show focal weak staining for hCG. Immunocytochemical identification of hCG and hPL has proved helpful in clarifying the histogenesis of trophoblastic neoplasms and may also be of value in establishing their diagnosis and in determining their prognosis.