A Case Report of ZC3H7B-BCOR High-grade Endometrial Stromal Sarcoma Expressing CD117 and DOG1: A Molecularly Confirmed Diagnostic Pitfall

High-grade endometrial stromal sarcoma (HGESS) is a rare sarcoma with aggressive biological behavior. Here we report a case of molecularly confirmed ZC3H7B-BCOR HGESS in extrauterine, with morphologic and immunohistochemical findings resembling a gastrointestinal stromal tumor. The patient, a 51-year-old woman, presented with extensive pelvic and abdominal masses. Histologically, the tumor displayed fascicles of spindle cells with myxoid stroma and abundant mitosis. Immunohistochemical staining revealed that the tumor cells were diffusely positive for cluster of differentiation 117 (CD117) and discovered on gastrointestinal stromal tumor 1 (DOG1). Gastrointestinal stromal tumor was initially diagnosed, and DNA sequencing was performed for targeted therapy. Unexpectedly, no mutations in KIT proto-oncogene, receptor tyrosine kinase (CKIT) or platelet-derived growth factor receptor, alpha polypeptide (PDGFRA) were identified, but amplification of murine double minute 2 (MDM2) and cyclin-dependent kinase 4 (CDK4) was found. Further, ZC3H7B-BCOR fusion was detected via RNA sequencing. Additional immunostaining showed that CD10 was diffusely positive, the estrogen receptor was negative, and the progesterone receptor was weakly positive. ZC3H7B-BCOR HGESS was definitively diagnosed. In conclusion, the coexpression of CD117 and DOG1 may present a potential diagnostic pitfall in the evaluation of pelvic/abdominal masses, which should be paid great attention.