262 Metastatic Low-Grade Endometrial Stromal Sarcoma to the Breast Years After Hysterectomy: A Case Report

Introduction/Objective Metastatic low-grade endometrial stromal sarcoma (LG-ESS) is uncommon and can occur years after primary diagnosis and/or hysterectomy. Rarely, LG-ESS can metastasize to the breast, mimicking primary breast spindle cell lesions. Methods/Case Report We present a case of a 68-year-old female with a remote history of a hysterectomy and bilateral salpingo-oophorectomy (TAH-BSO), who was found to have a left breast mass on screening mammography. Diagnostic mammogram showed a 0.4 cm mass with indistinct and micro-lobulated margins in the upper outer quadrant. Histologic evaluation demonstrated an irregularly contoured lesion surrounded by a dense fibrous rim and composed of plump, whorled, monomorphic spindle cells and prominent arterioles. The tumor cells expressed ER, PR, WT-1, and diffuse CD10, supportive of metastatic LG-ESS. Immunohistochemical stains CD34, STAT6, beta-catenin, pankeratin, keratin 5/6, p63, ERG, and S100 were negative, excluding primary spindle cell lesions of the breast. The diagnosis was confirmed by fluorescence in situ hybridization (FISH), which demonstrated a JAZF1 gene rearrangement. Subsequent review of the hysterectomy specimen, originally diagnosed as cellular leiomyoma, showed similar morphological features, consistent with primary LG-ESS Results NA Conclusion Our case report highlights the importance of a thorough chart review, radiologic findings, careful morphologic and immunophenotypic evaluation, and and cytogenetic testing in making this diagnosis.