Extrauterine low-grade endometrial stromal sarcoma with florid endometrioid glandular differentiation.

Endometrial stromal sarcoma of the uterus (ESS) is a rare lesion that can cause diagnostic difficulty especially when it presents with unusual histologic features such as diffuse endometrioid glandular differentiation. Only three such cases have been reported, all primary in the uterus. We report the first case of an extrauterine low-grade ESS with extensive glandular differentiation that appeared to arise in endometriosis.