Uterine sarcoma is a very rare kind of cancer that forms in the uterine muscles or in tissues that support the uterus. Uterine sarcoma is different from cancer of the endometrium, a disease in which cancer cells start growing inside the lining of the uterus
Exposure to x-rays during radiation therapy can increase the risk of uterine sarcoma. Another risk factor for uterine sarcoma is treatment with tamoxifen for breast cancer. If you are taking this drug, have a pelvic exam every year and report any vaginal bleeding, other than menstrual bleeding, as soon as possible.
Source: National Cancer Institute