Epithelioid trophoblastic tumor: Morphological and immunohistochemical study of three lung lesions

Epithelioid trophoblastic tumor (ETT) is a term proposed for an unusual var iant of trophoblastic tumor that is closely related to choriocarcinoma but shows monomorphic growth of highly atypical trophoblastic cells instead of the typical dimorphic pattern of choriocarcinoma. We report here 3 cases of ETT, all of which were lung lesions probably originating from uterine trop hoblastic disease. The antecedent pregnancies of the 3 cases were hydatidif orm mole, invasive mole, and term pregnancy, respectively. The tumors were composed of highly atypical mononucleate cells, which mainly involved alveo lar spaces, forming nests with central eosinophilic necrosis. Multinucleate giant cells were found within the nests, but they were fewer in number tha n in typical choriocarcinoma. The tumors were not associated with extensive hemorrhage or necrosis, except for 1 case, in which the ETT was combined w ith typical dimorphic choriocarcinoma. Immunohistochemically, multinucleate giant cells and occasional mononucleate tumor cells showed positivity for human chorionic gonadotropin. Staining for human placental lactogen was pos itive in rare multinucleate giant cells, and in 1 case, tumor cells showed diffuse positivity for placental alkaline phosphatase. Because ETT has a re markably epithelioid appearance in cytological and architectural features, differentiation from the epithelial malignancies is problematic. Trophoblas tic markers are frequently expressed in nontrophoblastic tumors, and reacti vity for those markers alone is not sufficient for exclusion of other tumor s. Rather, evidence of ETT comes from a combination of morphological featur es, immunohistochemical study, and clinical history. Copyright (C) 1999 by W.B. Saunders Company.