Mucoepidermoid carcinoma metastatic to the skin. An histologic mimic of a primary sweat gland carcinoma.

Mucoepidermoid carcinomas are tumors that usually arise from salivary glands and have a characteristic histologic pattern of atypical squamous cells showing focal mucin production. Mucoepidermoid carcinomas are uncommon neoplasms that metastasize most commonly via lymphatic and hematogenous channels. We report what we believe to be the first case of a mucoepidermoid carcinoma arising from a sublingual salivary gland with metastasis to a distant site on the skin. The patient is a 58-year-old black woman who was initially diagnosed with a high grade mucoepidermoid carcinoma of the salivary glands of the tongue. Approximately 18 months after presentation, and 6 months following surgery, chemotherapy, and radiation therapy, the patient noted a firm nodule on her flank. Biopsy showed malignant squamous epithelium. Periodic acid-Schiff and alcian blue stains revealed focal mucin production. The histologic differential diagnosis included an eccrine carcinoma, mucin-producing adenocarcinoma with squamous differentiation, a primary cutaneous adenosquamous (mucoepidermoid) carcinoma and a malignant mixed tumor of the skin. Clinical correlation was essential in making the correct diagnosis. While mucoepidermoid carcinomas only uncommonly show distant metastasis, and even less frequently involve the skin, this entity should be included in the differential diagnosis of mucin-producing neoplasms in the skin.