Primary Low-Grade Endometrial Stromal Sarcoma of the Ovary Arising From Endometriosis: A Case Report

Low-grade endometrial stromal sarcoma (LGESS) is a rare mesenchymal tumor of female genital tract malignancies. While it primarily arises in the uterus, extrauterine cases, including those originating in the ovary, are exceedingly rare. While there is a hypothesis that endometriosis plays a role in the development of extrauterine cases, the diagnosis of primary ovarian LGESS is challenging due to its rarity and similarity to metastatic uterine LGESS. A 52-year-old premenopausal woman with a history of adenomyosis was referred for an enlarging left ovarian endometriotic cyst, raising suspicion of malignancy. Transvaginal ultrasound revealed a 100×50 mm left ovarian mass with a 30 mm thick cystic component. MRI indicated a solid-cystic tumor with features suggestive of an endometriotic cyst. Positron emission tomography-computed tomography (PET-CT) revealed mild fluorodeoxyglucose (FDG) uptake with a maximum standardized uptake value (SUVmax) of 3.05, with no evidence of distant metastases. Primary debulking surgery was performed. Intraoperatively, the left ovary was enlarged (10 cm) with peritoneal dissemination. A frozen section suggested a granulosa cell tumor. The patient underwent total hysterectomy, bilateral salpingo-oophorectomy, subtotal omentectomy, and high anterior rectal resection. Histopathology revealed a proliferation of small, uniform tumor cells resembling proliferative endometrial stroma adjacent to an area of ovarian endometriosis. Immunohistochemical analysis showed positivity for estrogen receptor (ER), progesterone receptor (PgR), and CD10, confirming LGESS. The final diagnosis was the International Federation of Gynecology and Obstetrics (FIGO) Stage IIIB (pT3bNxM0). Postoperatively, the patient was treated with medroxyprogesterone acetate (MPA) at 600 mg/day, later reduced to 400 mg/day due to weight gain. She remains recurrence-free three years post-treatment. Primary ovarian LGESS is rare and often difficult to distinguish from metastatic uterine LGESS. The presence of endometriosis suggests a link to chronic inflammation and estrogen stimulation in tumorigenesis. Strong ER/PgR positivity highlights its endocrine-dependent nature, making hormonal therapy an effective option. MRI findings, including high T1 signal, low T2 signal, and heterogeneous enhancement, may aid in diagnosis, especially when combined with endometriosis. Optimal cytoreductive surgery improves prognosis, and complete resection of disseminated lesions likely contributed to this patient's favorable outcome. Hormonal therapy plays a crucial role in preventing recurrence, though long-term management must consider adverse effects. This case highlights the importance of considering LGESS in ovarian tumors associated with endometriosis. A combination of optimal surgery and hormonal therapy is key to long-term remission. Close monitoring of ovarian endometriosis patients is essential due to the risk of malignant transformation.