Cytogenetic and clinicopathologic studies of partial moles.

Fifty-six partial moles from 55 patients were karyotyped and analyzed clinicopathologically. Forty-seven were triploid and nine diploid. Triploid partial moles were characterized histologically by focal mild-to-moderate trophoblastic hyperplasia with stromal trophoblastic inclusion. Diploid partial moles lacked marked trophoblastic hyperplasia and stromal trophoblastic inclusions. Four of the nine diploid moles were analyzed for chromosome heteromorphisms, enzyme polymorphisms, and histocompatibility leukocyte antigen specificities to determine their origin, and two were found to be normal. In the follow-up study, none of the partial moles developed into invasive mole or choriocarcinoma. These results indicate that most partial moles are triploid but a minority are normal diploid; regardless of the karyotype, however, partial moles do not have a high propensity for malignancy.