Primary intraplacental gestational choriocarcinoma: histologic and genetic analyses.

Gestational choriocarcinoma is a highly malignant form of gestational trophoblastic tumors. Placental involvement of the tumor is exceedingly rare. We describe a case of intraplacental choriocarcinoma in a full-term placenta. Microscopically, there were sheets of highly pleomorphic trophoblasts invading the placenta, leaving isolated chorionic villi within the tumor. We utilized molecular genetic methods to determine the genotype of the tumor and compared it with that of the placenta. Short tandem repeat polymorphism analysis was performed on tumor and placental DNA macrodissected from unstained slides of formalin-fixed, paraffin-embedded tissue. The assay included polymerase chain reaction reactions of 10 polymorphic genetic loci. Comparing the polymorphic genetic markers of the tumor with the placenta revealed a complete match in the genotype of all loci examined. The results suggest that the choriocarcinoma originated from the current placenta sharing exactly the same genotype of multiple polymorphic markers. It also excludes a nongestational choriocarcinoma, which is of germ cell origin.