Lin DI, Huang RSP, Mata DA, et al. - Studies have described BCORL1 as a transcriptional corepressor homologous to BCOR. Researchers herein report 12 BCORL1-altered uterine sarcomas with striking resemblance to BCOR-altered endometrial stromal sarcoma (BCOR-ESS). These included 5 with BCORL1 rearrangements (JAZF1-BCORL1, EP300-BCORL1, or internal BCORL1 rearrangement), 5 with inactivating BCORL1 mutations (T513fs*22, P600fs*1, R945*, R1196*, or R1265fs*4) and 2 with homozygous BCORL1 deletion. The patients were of median age of 57.5 years (range 33–79). Observations suggest an association with aggressive clinical behavior. Prior to genomic testing, various diagnoses were assigned: 7 tumors were previously diagnosed as ESS, 2 as high-grade uterine sarcomas, 2 as myxoid uterine leiomyosarcomas, and 1 as a uterine spindle cell neoplasm consistent with leiomyosarcoma. Gross examination revealed frequent gelatinous, mucomyxoid-like appearance of the tumors. Following were identified as the key microscopic features (1) a spindle cell appearance, most often with at least focal myxoid stroma, (2) variable amounts of hypocellular fibromyxoid spindle areas with lower grade atypia and/or (3) variable amounts of epithelioid areas with higher grade atypia. Overall findings suggest that inactivating BCORL1 genomic alterations may define a different subset of high-grade endometrial stromal sarcomas with biological overlap with BCOR-ESS, both of which may mimic myxoid leiomyosarcomas.