Advances in the understanding of placental site trophoblastic tumor.

Placental site trophoblastic tumor (PSTT) is the least common form of gestational trophoblastic disease. The tumor represents a neoplastic transformation of intermediate trophoblastic cells that normally play a critical role in implantation. PSTT can occur after a normal pregnancy, spontaneous abortion, termination of pregnancy, ectopic pregnancy or molar pregnancy. It displays a wide spectrum of behavior, and when metastatic, can be difficult to control even with surgery and chemotherapy. Because of PSTT's rarity, limited information is known about its natural history. Several recent studies have indicated that mitotic index is an important prognostic indicator. Advances in chemotherapeutic regimens have also improved clinical response in metastatic disease.