Bilateral Ovarian Mass: Low-Grade Endometrial Stromal Sarcoma—a Rare Entity Ruchit Shah, DNB, Shilpi Bhargava, MD, * Deepa Wadhwani, DPB, Mansi Faujdar, MD, { and Shubha Gupta, MD Abstract Background: An endometrial stromal tumor is a histopathologic entity characterized by a monomorphus pop- ulation of blunt, spindle-to-oblong–shaped cells with scant cytoplasm in an abundant reticulin framework. This entity was first described in 1908, and was well-characterized by Norris and Taylor in 1966. It is classified as: (1) a benign stromal nodule; (2) a low-grade endometrial stromal sarcoma; or (3) an undifferentiated endometrial sarcoma. Endometrial stromal sarcomas usually arise from the uterine corpus. The most common extrauterine site is the ovary. Case: A 50-year-old female presented clinically with an abdominal lump. Radiologic findings were inconclusive and suggestive of a bilateral ovarian mass. Microscopic examination revealed a circumscribed tumor composed of uniform cells, having scanty cytoplasm, and having uniform nuclei showing nest and sex-cord differentiation that was seen blending with intervening stromal cells. Results: Immunoreactivity of tumor cells for cluster of differentiation (CD10) and stromal cells confirmed the most rare diagnosis of an endometrial sarcoma in the ovary. Patient was well on regular follow up and after surgical correction. Conclusions: Given that endometrial stromal sarcomas frequently express estrogen and progesterone receptors, treatment with hormonal therapies may be efficacious for patients with advanced, residual, and recurrent cases. ( J GYNECOL SURG 31:351) Introduction A n endometrial stromal sarcoma is a rare malignant tumor that constitutes *0.2% of all uterine malignan- cies. 1 The endometrial stroma gives rise to neoplasms that resemble normal stromal cells closely. The cells are uniform in size and have scanty amounts of cytoplasm. An endome- trial stromal sarcoma occurring in an extrauterine site is rare in the absence of metastasis or extension of a primary uterine tumor. 2 The ovary is the most frequent extrauterine site, which occurs in 76% of cases. 3 Case A 50-year-old female presented clinically with abdominal pain and fullness. On examination, the abdominal lump was palpable. This patient had undergone a hysterectomy a few years prior in another primary institute, but there were no previous histopathologic reports. Radiologic findings revealed solid, well-circumscribed masses involving both ovaries and measuring 7 · 6cm. The masses extended up to the obturator foramen, and there were pelvic nodules. Intraoperatively, the masses were seen involving both ova- ries and obturator foramen with pelvic peritoneal implants. Total resection of the masses, including oopherectomy, was performed, and samples were sent for histopathologic exami- nation. Grossly the left and right ovarian masses measured 7 cm and 6 cm, respectively, and were solid in consistency. A cut surface was a solid greyish-white. The obturator foramen mass mea- sured 5cm and had the same gross features as the ovarian masss. Representative sections were taken from tumor tissue. On microscopic examination, a well-circumscribed tumor composed of uniform cells showing heterologous differen- tiation and having scanty cytoplasm, uniform nuclei, mini- mal atypia, and few mitotic figures. The stromal cells were bipolar and were arranged in nests and a trabecular pattern, showing sex-cord differentiation. Features showing nest and sex-cord differentiation blended with intervening stromal cells (Fig. 1) in the background with extensive hyalinization at various places (Fig. 2). The neoplastic cells were immunoreactive to cluster of differentiation (CD10; Fig. 3) and progesterone receptor (PgR), and were negative for h-Caldesmon, cytokeratin, endomysial antibodies (EMA), calretinin, inhibin, MelanA, CD34 protein, and S-100 protein. The sex-cord elements expressed desmin (Fig. 4) and smooth-muscle antibodies Department of Pathology, Santokba Durlabhji Memorial Hospital, Jaipur, India. *Current affiliation: Pt. Bhagwat Dayal Sharma Post Graduate Institute of Medical Science, Rohtak Haryana, India. {Consultant. JOURNAL OF GYNECOLOGIC SURGERY Volume 31, Number 6, 2015 ª Mary Ann Liebert, Inc. DOI: 10.1089/gyn.2015.0002 351