Placental site trophoblast tumours (PSTTs) were originally described in 1976  and are the least common type of gestational trophoblast disease forming less than 2% of all cases. PSTT most commonly follows a normal pregnancy but can also occur after a non-molar abortion or a complete molar pregnancy, and very rarely following a PM.
In contrast to themorecommon types of trophoblast disease which characteristically present fairly soon after the index pregnancy, in PSTT the average interval between the prior pregnancy and presentation is 3.4 years. The most frequent presentation is bleeding following amenorrhea and the hCG level, while elevated, is characteristically lower for the volume of disease than in the other types of gestational trophoblastic tumour (GTT). The tumour is diploid and arises from the non-villous trophoblast and the pathology is characterized by intermediate trophoblas-tic cells with vacuolated cytoplasm, the expression of placental alkaline phosphotase (PLAP) rather than hCG and the absence of cytotrophoblast and villi.
The clinical presentation of PSTT can range from slow growing disease limited to the uterus to more rapidly growing metastatic disease that is similar in behaviour to choriocarcinoma.
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