ABSTRACT
Placental site trophoblastic tumor (PSTT), also known as atypical choriocarcinoma, syncytioma, chorioepitheliosis or trophoblastic pseudotumor, is a rare gestational trophoblastic disease (0.25-5% of all trophoblastic tumors) and it is composed by neoplastic proliferation of intermediate trophoblasts at placental implantation site. It consists of aggregates or sheets of large, polyhedral to round, predominantly mononucleated cells with a characteristic vascular and myometrial invasion. Main differential diagnoses are gestational choriocarcinoma (GC) and epitelioid trophoblastic tumor (ETT). We present a case of PSTT in a 25-year-old woman. Neoplastic cells showed moderate/high nuclear pleomorphism, abundant amphophilic, eosinophilic and clear cytoplasm, numerous mitotic figures (10 mitoses/10 HPF), and myometrial invasion. Other features are necrosis, vascular invasion with replacement of myometrial vessels by tumor cells and hemorrhage. The patient showed typical low serum ß-hCG levels and high serum humane placental lactogen (hPL) levels.