Clear cell myoepithelial neoplasm of the breast.

Primary clear cell tumors of the breast are rare neoplasms. Traditionally, their differential diagnosis has included lipid-rich, glycogen-rich, and secretory carcinomas of the breast. Although clear cell myoepithelial tumors of the salivary gland and skin have been reported, a primary clear cell myoepithelial carcinoma of the breast has not been previously described. We report a case of clear cell myoepithelial neoplasm of the breast showing an infiltrative histologic growth pattern highly suggestive of carcinoma. Electron microscopy showed evidence of myoepithelial differentiation manifested by cytoplasmic microfilaments with randomly dispersed fusiform densities in conjunction with specialized membrane junctions and remnants of basal membrane. Immunohistologically, the tumor cells were positive for actin, keratin, and S-100 protein. This tumor should be included in the differential diagnosis of the clear cell neoplasms of the breast.