Malignant rhabdoid tumor of the uterus.

Rhabdoid tumors are highly malignant neoplasms resembling rhabdomyosarcomas, which most commonly occur in the kidney in young children. Several cases of extrarenal malignant rhabdoid tumors have been described, many in adolescents and young adults. We describe a 46-year-old woman with a primary uterine tumor that has the histologic, immunohistochemical, and ultrastructural characteristics of a malignant rhabdoid tumor. To our knowledge, this is the first report of a rhabdoid tumor in this site. Furthermore, this woman's age expands the range for which pathologists and clinicians should consider this diagnosis, even in extrarenal sites.