Pigmented mucoepidermoid carcinoma of the oral cavity: a case report.

Melanocytes are normally present in the oral mucosa, but unlike the skin, melanocytic colonization and pigmentation of nonmelanocytic tumors rarely occur. A case of pigmented mucoepidermoid carcinoma (MEC) in a 36-year-old woman is reported. On H&E-stained sections, brownish granules were seen in intermediate and epidermoid neoplastic elements and in elongated or dendritic cells showing histologic and immunohistochemical features of melanocytes. Ultrastructurally numerous epithelial cells contained large aggregates of melanin granules, a feature suggestive of phagocytosis. In addition small individual melanin granules were observed at the external border of the epithelial cell membrane. These features suggest that melanocytes colonized the MEC and that neoplastic cells may phagocytose the granules, similarly to what occurs with epidermal melanocytes. The phenomenon of melanocyte colonization of nonmelanocytic tumors should be taken into consideration in dealing with pigmented lesions of the oral cavity.