Cutaneous syncytial myoepithelioma with folliculocentric growth and EWSR1 gene rearrangement: A case report.

Cutaneous syncytial myoepithelioma is a tumor type that was initially reported in 2013 as a syncytial variant of cutaneous myoepithelioma characterized by intradermal nodular proliferation of oval to spindle-shaped tumor cells in solid and syncytial patterns. Fusion of genes Ewing sarcoma breakpoint region 1 / EWS RNA binding protein 1 (EWSR1) and pre-B cell leukemia homeobox 3 (PBX3) is found in approximately 90% of the cases. We report a case of cutaneous syncytial myoepithelioma with diagnostic difficulty due to folliculocentric morphology and atypical immunohistochemical results, including diffuse positivity of α-smooth muscle actin and claudin 4 and negative immunoreactions for epithelial membrane antigen and S100 protein. In the present case, fluorescence in situ hybridization study demonstrated EWSR1 rearrangement. We further provide a discussion of differential diagnoses with a review of relevant literature.