Vagina, Biphasic synovial sarcoma, H&E stain

Synovial sarcoma is a malignant neoplasm of uncertain differentiation, most commonly characterized by a fusion gene associated with a translocation of chromosomes 18 and X. The slide shows a submucosal biphasic tumor composed of loose hypocellular areas alternating with hypercellular areas of spindle cells. Another component of benign-appearing epithelial cells forming glands and papillary projections is also present. Mitotic count is 19/10 HPF. The differential diagnosis in this case includes mullerian adenosarcoma, endometrial stromal sarcoma with epithelial component, and biphasic synovial sarcoma. The Illumina RNA Fusion panel analysis showed a translocation for the SS18-SSX1 genes, confirming the diagnosis of synovial sarcoma in this setting.