Rhabdomyosarcoma of the uterus: report of two cases, including one of the spindle cell variant.

Most uterine sarcomas fall into the category of leiomyosarcoma, endometrial stromal sarcoma, or undifferentiated sarcoma. Pure rhabdomyosarcomas are extremely rare, although a rhabdomyosarcomatous element may be present as a component of an adenosarcoma or carcinosarcoma (malignant mixed müllerian tumor). This report describes two uterine rhabdomyosarcomas in 28- and 67-year-old women. These were of spindle cell and pleomorphic types, respectively. At presentation the pleomorphic rhabdomyosaroma was stage IV, exhibiting massive pelvic and abdominal dissemination that mimicked an ovarian neoplasm. The spindle cell rhabdomyosarcoma was stage I, being confined to the uterus. Grossly, both uterine tumors had a polypoid appearance. Immunohistochemically, tumor cells were positive with the skeletal muscle markers sarcomeric actin, myoglobin, and myoD1. The patient with stage IV disease died within a short time of diagnosis and the other patient is alive and well at 2 years' follow-up. This report adds to the published literature on uterine rhabdomyosarcomas. This is the first reported uterine case of the spindle cell variant of embryonal rhabdomyosarcoma. Based on these cases and the published literature, rhabdomyosarcoma, especially the pleomorphic variant, appears to be a very aggressive neoplasm with an extremely poor prognosis. Immunohistochemical demonstration of skeletal muscle differentiation is necessary for a definitive diagnosis.