Intestinal and liver involvement by endometrial stromal sarcoma: Expanding the differential diagnosis of mesenchymal tumors involving the GI tract.

Endometrial stromal sarcoma (ESS) is a mesenchymal tumor known for infiltrative growth and lymphovascular invasion. Most examples arise in the endometrium, but some occur in the abdominal cavity without a primary uterine lesion, likely originating from endometriosis. ESS involving the gastrointestinal (GI) tract and liver is rare. We reviewed 15 examples from 13 women between 2010 and 2023. The mean age was 51 (range 16-81); just over half of the patients (7/13, 54 %) had a history of uterine ESS. Twelve tumors involved the intestines and three the liver; rectosigmoid colon was the most affected site. Tumors averaged 4.6 cm (range 0.3-10 cm) and involved all bowel layers with two showing transmural involvement. Predominantly low-grade features were observed, including uniform round to spindle cells in fibrous or myxoid stroma, permeative growth, hyaline plaques, and spiral arterioles. Endometriosis was seen in 4 (27 %) cases. Immunohistochemical analysis revealed positivity for ER (93 %), PR (92 %), CD10 (91 %), and focal cyclin D1 (80 %). A minority of cases showed staining with smooth muscle markers, CD117, DOG1, and keratins. High-grade features were suggested but not diagnostic in three cases. Follow-up data for three patients showed one death at 16 months, one patient disease-free at 94 months, and another alive at 16 months. ESS involving the GI tract is rare, may lack a uterine primary, and can mimic other neoplasms due to keratin, smooth muscle, and CD117/DOG1 expression. Recognizing ESS-associated features-such as a permeative pattern, hyaline plaques, and spiral arterioles-is key to avoiding misdiagnosis.