Extrauterine Undifferentiated Uterine Sarcoma Arising from Bladder Endometriosis in a Postmenopausal Woman: A Case Report.

Endometriosis (EMS) is a rare condition in postmenopausal women. The incidence of transition from EMS to malignancy is as low as 1%, with endometrial stromal tumors (ESTs) occurring at an even lower incidence of 0.7%. Undifferentiated uterine sarcomas (UUSs) are a subtype of ESTs that account for 25% of all ESTs. Extrauterine UUSs are exceptionally rare, with only a few reported cases in the literature. We present the case of a woman who underwent surgery for deep infiltrating EMS and was later diagnosed with UUS, which originated from the bladder after surgical menopause.