MED12 mutations were detected in 54% of classical uterine leiomyomas (15/28) and in 15% of cases in myometrium adjacent to leiomyomas (2/13); 34% of leiomyoma/leiomyomatosis in pelvic/retroperitoneal sites (10/29); 0% of extrauterine leiomyomas (0/29); 8% of smooth muscle tumor of uncertain malignant potential (1/12); 30% of uterine leiomyosarcomas (6/20); and 4% of extrauterine leiomyosarcomas (1/25).