Morphological, immunohistochemical, molecular and clinicopathological features of high grade endometrial stromal sarcomas

High grade endometrial stromal sarcoma (HG-ESS) is a malignant mesenchymal tumor of uterus which frequently demonstrates YWHAE-NUTM2 fusion. Previous studies identified HG-ESS cases with BCOR gene translocations. We thus aimed to investigate YWHAE and BCOR translocation and immunhistochemical BCOR expression status in HG-ESS from our archive and describe their clinical, laboratory and histopathologic features. One hundred ninety-four uterine sarcomas which were diagnosed between 2000-2019 were reevaluated. Thirty-nine cases which have specific features were included in this study. Fluorescent in situ hybridization (FISH) studies using YWHAE and BCOR brake-apart probes and immunohistochemical studies for BCOR, CD99 and CD56 were performed. BCOR IHC is also performed on 20 leiomyosarcomas which have classical features. Six patients had translocations involving YWHAE or BCOR. Five tumors showed high-grade morphology and revealed YWHAE translocation. One case with myxoid morphology revealed BCOR translocation. In immunohistochemistry, all except one YWHAE transloncated tumors showed BCOR, CD99 and CD56 positivity, however, BCOR translocated tumor was BCOR and CD56 negative. Four patients died 4, 18, 20 and 34 months after diagnosis, two were lost to follow-up. HG-ESS is an aggressive tumor with poor clinical outcome. Our study showed that BCOR immunohistochemistry could be a useful diagnostic tool to identify HG-ESS cases with translocation of YWHAE gene. However, BCOR immunohistochemistry could be positive in other entities, so that FISH analysis is essential for definitive diagnosis. We also report that molecular analysis and conspicuous myxoid morphology can help identifying HG-ESS with translocation of BCOR gene which could be negative with BCOR immunohistochemistry.