Pleomorphic Adenoma Misinterpreted as Mucosal Melanoma: A Case Report and Literature Review

Pleomorphic adenoma is the most common benign salivary gland neoplasm, yet it can histologically mimic mucosal melanoma, an aggressive and rare cancer associated with poor prognosis. Misinterpretation of pleomorphic adenoma as mucosal melanoma can result in unnecessary medical treatment and can lead to undue stress for the patient. Here we present a case of a 54 year-old woman with a history of chronic rhinosinusitis who was incidentally found to have a left palatal mass. The initial incisional biopsy and subsequent resection demonstrated histologic features consistent with mucosal melanoma, including positive S100 and Sox10 stains and focally positive areas of MelanA. However, upon second review and additional work-up a biphasic pattern and strong cytokeratin staining were identified, resulting in a final diagnosis of pleomorphic adenoma.