A sarcoma of the body of the uterus arising in older women, composed of more than one mesenchymal tissue, especially including striated muscle cells. It is associated with previous pelvic radiation exposure in 20% of patients. (Stedman, 25th ed; Holland et al., Cancer Medicine, 3d ed, p1702). The disease is EFO_1001371 (Mixed Tumor, Mesodermal).