Histological features of gestational trophoblastic neoplasms. Choriocarcinoma is characterized by biphasic growth pattern composed of syncytiotrophoblast and mononucleate trophoblastic cells, forming vasculogenic mimicry. Placental site trophoblastic tumor (PSTT) is composed of confluent masses of neoplastic intermediate (extravillous) trophoblastic cells, infiltrating within smooth muscle cells. Epithelioid trophoblastic tumor (ETT) contains neoplastic chorionic-type intermediate (extravillous) trophoblastic cells surrounding an artery. Lack of a y-chromosomal complement in the majority of gestational trophoblastic neoplasms. Yap KL, Hafez MJ, Mao TL, Kurman RJ, Murphy KM, Shih IeM - Journal of oncology (2010). Not Altered. CC.