Malignant Transformation of Endometriosis: A Rare Case of Extrauterine Endometrial Stromal Sarcoma

Endometrial stromal sarcoma (ESS) is an extremely uncommon uterine malignancy, and commonly arises from preexisting endometriosis. On rare occasions, ESS arises from extrauterine tissues and is known as extra-uterine ESS. This case report focuses on a 31-year-old woman who presented with chronic pelvic pain secondary to extensive deep-infiltrating endometriosis. Pelvic ultrasound revealed the presence of bilateral endometriomas with extensive endometriosis infiltrating segments of bowel and ureter. This was confirmed on laparoscopic exploration. Consequently, a series of surgical procedures were performed for excision of endometriosis, which included left nephroureterectomy, bowel resection with defunctioning loop ileostomy, subtotal hysterectomy, and bilateral salpingo-oophorectomy. Histological examination identified estrogen and progesterone receptor positive low-grade ESS alongside endometriosis in the omentum, large bowel, and ovaries. The disease was primarily extrauterine, with no involvement of the uterus. Following debulking surgery, the patient was commenced on adjuvant hormonal therapy to suppress the disease. This rare case highlights that existing chronic endometriotic lesions have the potential to transform into malignancy, and clinicians must be aware of this. Clinical manifestation and radiological features of ESS are the same as endometriosis and diagnosis is based on histopathological evaluation.