Endometrial stromal sarcoma of the sigmoid colon: a case report and literature review.

Endometrial stromal sarcoma (ESS) is a rare mesenchymal tumor of the uterus that accounts for 7-25% of uterine sarcomas and < 1% of uterine tumors. Previously reported sites include the ovary, bowel wall, abdomen, peritoneum, pelvis, and vagina; however, ESS in the extrauterine area is rare. We report a rare case of endometrial stromal sarcoma that developed in the sigmoid colon along the gonadal vasculature, which was difficult to distinguish from colon cancer. A large polyp was found in the sigmoid colon of a 74-year-old woman during a routine medical examination and was diagnosed as tubular adenoma. On colonoscopy 7 months later, the tumor had grown and blocked the lumen, causing stenosis. She was referred to our hospital for surgery. Although detailed examination at our hospital did not yield a definitive diagnosis, bowel obstruction was considered likely and we performed laparoscopic low anterior resection under a preoperative diagnosis of sigmoid colon cancer. The tumor protruded into the sigmoid colon from the stump of the ovarian arteries and veins outside the intestinal tract. As the left ovarian artery and vein were involved in the tumor, we extracted them as a lump. The tumor was diagnosed as low-grade ESS (LG-ESS). She had a history of hysterectomy and left salpingo-oophorectomy for uterine myoma 25 years ago, and radiation therapy was performed after surgery for an unknown reason. The postoperative course was uneventful, and follow-up was continued at the request of the patient. We report a rare case of ESS infiltrating the sigmoid colon, which was probably a lesion derived from endometriosis of the ovarian arteriovenous stump remaining after surgery 25 years ago. © The Japan Society of Clinical Oncology 2021.