Current issues in the histopathology of gestational trophoblastic tumors

Gestational trophoblastic neoplasia (GTN) encompasses several entities including complete (CHM) and partial (PHM) hydatidiform mole (HM) and the malignant gestational trophoblastic tumors (GTTs), choriocarcinoma (CC), and placental-site trophoblastic tumor (PSTT), including epithelioid trophoblastic tumor (ETT). To detect pGTN, postmolar surveillance by measurement of maternal human chorionic gonoadotropin (hCG) levels should be performed. With such a protocol, many cases of pGTN are identified early at a presymptomatic stage based on plateuing or rising hCG concentrations and subsequently treated successfully with chemotherapy. In such cases, histopathological confirmation of the precise nature of the pGTN usually is not available. However, GTT also may present clinically with primary or metastatic disease, either following and unrecognized HM or developing from a nonmolar gestation. Due to their distinctive clinical and histological features, malignant GTTs are generally clearly subdivided into CC and PSTT (including ETT). CC essentially represents malignant trophoblastic tumors with differentiation toward villous trophoblast, with extensive hematogenous spread and high hCG levels, which are highly chemoresponsive. However, PSTTs, represent malignant differentiation toward implantation-site type trophoblast, with lower hCG levels and less response to chemotherapy. Current issues regarding the clinical and histological features of CC and PSTT/ETT are discussed.