Placental site trophoblastic tumor is a very rare variant of gestational trophoblastic disease which differs histologically and immunocytochemically from gestational choriocarcinoma. The English language literature includes only 74 reported cases. Seventeen patients have been managed at Charing Cross Hospital with this diagnosis. The median follow-up is 4.6 years, and the 5-year overall survival is 80% (95% confidence interval, 55-93%). Multivariate regression analysis identified an interval of >2 years since the preceding pregnancy as an independent adverse prognostic factor. Genotypic analysis by PCR allelotyping has confirmed the gestational origin of all 11 tumors successfully studied. More detailed molecular analysis has identified the causative pregnancy for eight tumors. Five were diploid biparental tumors following term pregnancies, and three were androgenetic tumors following monospermic complete hydatidiform moles.

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