Primary mucoepidermoid carcinoma of the skin expressing p63

Primary mucoepidermoid carcinoma (MEC) of the skin is an unusual neoplasm with few cases reported in the English medical literature. It has to be differentiated from adenosquamous carcinoma, usually a high-grade neoplasm with poorer outcome, and metastasis from a primary MEC arising elsewhere in the body. We report a 78-year-old woman with an abdominal skin lesion of recent onset. Histopathological examination revealed a dermal located carcinoma with variable proportions of squamous differentiation and goblet cells. The patient died in a very short time for an unrelated disease. Immunohistochemical study showed staining for cytokeratins (AE1AE3, 7, and 34betaE12), epithelial membrane antigen (EMA), and p63, whereas cytokeratins 18 and 20 and gross cystic disease fluid protein (GCDFP15) were negative. We conclude that primary MEC of the skin is usually a slow-growing neoplasm that should be differentiated from adenosquamous carcinoma. The immunohistochemical staining for p63 is helpful to differentiate primary and metastatic MEC in the skin.