In situ choriocarcinoma arising in partial hydatidiform mole: implications for the risk of persistent trophoblastic disease.

The risk of persistent trophoblastic disease following partial hydatidiform mole is controversial. In spite of claims that 4 to 11% of cases require chemotherapy, there is a paucity of affected patients in the literature. A critical review of those patients suggests an alternative or unproven diagnosis in the majority. An instance of placental in situ choriocarcinoma arising in a partial mole is reported. Because in situ choriocarcinoma may represent the incipient lesion in the majority of the one-third of cases of gestational choriocarcinoma that follow a normal pregnancy, we postulate that the presence of the in situ lesion in a partial mole supports the view that the risk of persistent trophoblastic disease may be no greater after partial mole than after a normal gestation.