Intraplacental choriocarcinoma: a report of two cases.

Two examples of intraplacental choriocarcinoma are described. Both were small and had arisen in otherwise normal third trimester placentas. The covering mantle of many of the villi adjacent to the choriocarcinomas was formed, either focally or wholly, of neoplastic trophoblastic tissue: it is only at this stage of the development of a choriocarcinoma that villous structures are present, and a study of these cases adds further evidence for an origin of choriocarcinoma from villous trophoblast. Intraplacental choriocarcinomas can give rise to both maternal and fetal metastases during pregnancy, and it is suggested that such lesions also serve as an origin for those choriocarcinomas which follow a term pregnancy.