Recurrent mucinous carcinoma of skin mimicking primary mucinous carcinoma of parotid gland: a diagnostic pitfall.

A case of a 63-year-old man with a swelling lasting 2 years in the left infraauricular area is reported. Examination by fine needle aspiration cytology raised suspicion of mucoepidermoid or adenoid cystic carcinoma of the parotid gland and an excision was recommended. The lateral parotidectomy specimen showed a poorly circumscribed gelatinous tumor measuring 15 mm in diameter within the parotid gland tissue. Microscopically, the lesion featured large pools of mucin containing clusters of tumor cells with little atypia and low mitotic activity. Immunohistochemically, the tumor cells showed expression of epithelial markers and of both estrogen and progesterone receptors. Left lateral neck dissection revealed massive lymphogenous dissemination of the tumor. Retrospective analysis of a skin biopsy from the same anatomic area performed 8 years prior to parotid neoplasm displayed a tumor with identical microscopic appearance and immunohistochemical profile (additionally performed) which was, however, misdiagnosed as a benign lesion. The diagnosis of recurrent primary mucinous carcinoma of the skin infiltrating the parotid gland was established. The patient underwent radiotherapy and has been 3 years free of disease. The differential diagnostics of this rare tumor is discussed.