Previous hydatidiform mole identified as the causative pregnancy of choriocarcinoma following birth of normal twins.

For appropriate clinical management of patients with gestational trophoblastic tumors it is important to ascertain both the nature of the causative pregnancy and the time interval between that pregnancy and the diagnosis of the tumor. It has been shown that the immediately antecedent pregnancy may not be the causative pregnancy in some cases of choriocarcinoma, particularly where there is a history of molar pregnancy. We report further studies of a case where the causative pregnancy was shown to be a hydatidiform mole, not the immediately antecedent normal term pregnancy. We describe the use of the polymerase chain reaction (PCR) to amplify short tandem repeat polymorphisms in DNA prepared from pathologic blocks of the patient's previously recognised molar pregnancy. A comparison of these polymorphisms with those in the parental and tumor DNA has enabled us to confirm that this hydatidiform mole was indeed the causative pregnancy. Molecular genetic techniques provide a rapid method of determining whether a choriocarcinoma is gestational and, if so, identifying the causative pregnancy.