The Clinicopathologic Features of YWHAE-FAM22 Endometrial Stromal Sarcomas: A Histologically High-grade and Clinically Aggressive Tumor

Endometrial stromal sarcoma (ESS) is a genetically heterogenous group of uterine sarcomas, of which almost half are associated with JAZF1 rearrangement. We recently identified a novel genetic fusion between YWHAE and FAM22A/B in ESS harboring t(10;17)(q22;p13) and herein describe the clinicopathologic features of 13 YWHAE-FAM22 ESS cases (11 primary and 3 metastatic) and compare them with 20 ESS cases with JAZF1 rearrangement. Ten of 11 primary uterine tumors contained morphologically high-grade areas composed of round cells arranged in nests with a delicate stromal capillary network. The tumor cells showed large nuclei with irregular nuclear contours and significant mitotic activity (>10 mitoses/10 HPF) in addition to focal tumor necrosis, in contrast to JAZF1 ESS, which lacked a nested growth pattern, were composed of cells with small round/oval nuclei, and typically had <5 MF/10 HPF. In 7 of the 11 uterine tumors, there was an additional cytologically bland and mitotically weakly active spindle cell component with a fibrous/fibromyxoid stroma (ESS, fibromyxoid variant). Two metastatic tumors (pulmonary) also contained round cell and spindle cell components, whereas 1 metastasis (vaginal) was composed solely of the spindle cell component. In both primary and metastatic tumors, the spindle cells were diffusely positive for estrogen and progesterone receptors and CD10, in contrast to the round cell areas, which were negative. Clinically, 10 of 12 patients with YWHAE-FAM22 ESS presented with FIGO stages II to III disease, in contrast to only 4 of 16 patients with JAZF1 ESS presenting with stages II to III disease (P