Endometrial Stromal Sarcoma Arising in Colorectal Endometriosis.

The malignant transformation of endometriosis is very uncommon. Whereas 75% of tumors arising from endometriosis arise in the ovary, location in extra-genital organs is rare and mesenchymal neoplasms are exceptional. A 47 year-old woman who underwent hysterectomy with bilateral salpingo-ooforectomy due to endometriosis 13 years before presented with abdominal pain. The magnetic resonance imaging (MRI) showed a 9.7×7.5 cm solid-cystic supravesical mass and a recto-vaginal tumor, as well as endometriotic nodules in the sigma, right parametrium and peritoneum that had significantly increased in size over a six months period. The patient underwent surgical resection of the masses. The histological study showed a low-grade endometrial stromal sarcoma (ESS) arising from endometriosis located at recotovaginal septum and affecting colonic wall and multiple peritoneal and pelvic implants. The patient received radiotherapy and aromatase inhibitors and is free of disease after a follow up of 2 years. Only 15 cases of ESS arising in endometriosis of the bowel have been reported. Tumor dissemination at diagnosis is unusual but does not imply a poor prognosis, as only one patient has died due to progression of the tumor. ESS should be included in the differential diagnosis of mesenchymal neoplasms in the intestine.