In challenging cases, molecular analysis will identify the typical alterations in high-grade endometrial stromal sarcomas, including YWHAE::NUTM2A/B fusion, BCOR rearrangements, BCOR “ITD” (internal tandem duplications of different lengths involving exon 15), or fusions involving JAZF1 and/or PHF1 (in cases of low-grade endometrial stromal sarcomas with high-grade transformation) [1,15,29]. The gene discussed is BCOR; the disease is endometrioid stromal sarcoma.