Histomorphological and immunophenotypical spectrum of cutaneous myoepitheliomas: A series of 35 cases

Abstract

Myoepithelial tumors comprise a group of mesenchymal lesions that show heterogeneous histomorphological features, including dual epithelial, neural, and myoid differentiation. Cutaneous myoepithelioma is a rare neoplasm that is composed primarily of myoepithelial cells and represents one end of a histopathological spectrum of cutaneous myoepithelial neoplasms including chondroid syringoma and myoepithelial carcinoma. These tumors display a wide histopathological spectrum and immunophenotypical profile often showing epithelial and myoepithelial differentiation. In this series, we studied 35 cases of cutaneous myoepitheliomas. Our cases highlighted the broad histopathological range where most cases showed a non-infiltrative and non-encapsulated tumor exclusively located in the dermis and with no subcutaneous involvement. The majority of our cases had a solid growth pattern (syncytial pattern) and the remainder of cases had a multinodular growth pattern. The tumor cells were epithelioid in 23 cases, spindled in eight cases and there was a mixture of epithelioid and spindled cells in four cases. Mitotic figures ranged from 0 to 5 per 10 HPF. By immunohistochemistry epithelial membrane antigen (EMA) was expressed in 59% of cases S100 was positive in 88% of cases, CAM 5.2 was positive in 16% of cases, AE1/AE3 was positive in 44% of cases, p63 was positive in 17% of cases, smooth muscle actin was positive in 38% of cases, desmin was positive in 6% of cases, calponin was positive in 22% of cases, and glial fibrillary acidic protein was positive in 36% of cases. In addition, there were five cases without EMA, keratin, or p63 expression that only showed S100 expression. We describe a large series of cutaneous myoepitheliomas delineating their histomorphological spectrum and immunophenotypical profile. Awareness of some of the unusual histopathological features and the heterogeneous immunohistochemical may pose difficulties for the diagnosis.