Incidentally Discovered Intra-Abdominal Low-Grade Endometrioid Stromal Sarcoma Confirmed by JAZF1 Rearrangement Study.

Endometrial stromal tumors comprise a spectrum of lesions ranging from benign nodules to malignant sarcomas. Endometrial stromal sarcomas are classified as either low-grade or high-grade based on morphologic, immunophenotypic, and genetic features. The majority of low-grade endometrial stromal sarcomas of the uterus are characterized by recurrent chromosomal translocations producing specific gene fusions, with JAZF1::SUZ12 being the most common. While endometrial stromal sarcomas typically originate in the uterine corpus, the neoplasm can rarely manifest as an extrauterine tumor in the absence of uterine involvement (endometrioid stromal sarcoma or extrauterine endometrial stromal sarcoma). Herein, we present a case report of a 55-year-old woman presenting with an intra-abdominal mass incidentally found on renal ultrasound performed for chronic kidney disease. Resection revealed irregular nodules of tumor permeating mesenteric soft tissue, composed of small, uniform ovoid to spindled cells expressing CD10, estrogen receptor, and WT1. Gross and microscopic evaluation of the accompanying hysterectomy specimen showed no uterine involvement by the tumor. Fluorescent in-situ hybridization (FISH) study performed on the mesenteric mass demonstrated the presence of a JAZF1 gene rearrangement. The patient was diagnosed with low-grade endometrioid stromal sarcoma and placed on adjuvant hormone therapy without clinical or imaging recurrence at 18-month follow-up. This case report underscores the utility of FISH as a potential confirmatory diagnostic tool in specimens of suspected extrauterine endometrial stromal sarcoma.