Implantation site on a cellular leiomyoma: a light microscopic and immunohistochemical study.

A case of gestational implantation upon a submucosal cellular leiomyoma in a 43-year-old woman is presented. The resulting histologic picture resembled placental site trophoblastic tumor (PSTT). In immunoperoxidase studies, tumor cells were positive for desmin and vimentin and negative for human placental lactogen and human chorionic gonadotropin, thus supporting a smooth muscle origin. This case demonstrates an unusual histological picture occurring in a setting that might lead to diagnostic confusion and is one in which immunohistochemical evaluation proved to be of great utility.