Benign Parotid Myoepithelioma: A Diagnostic Chameleon Masquerading as Pleomorphic Adenoma and the Critical Role of Immunohistochemistry

Myoepithelioma is a rare benign salivary gland tumor (<1%) that poses a significant diagnostic challenge by perfectly mimicking pleomorphic adenoma on imaging. We report a case of a 56-year-old male with a slow-growing, painless left parotid mass. MRI findings were typical for pleomorphic adenoma. The patient underwent superficial parotidectomy. Histopathology revealed a proliferation of myoepithelial cells, and immunohistochemistry (p63+, CK7+, S100+, EMA−) was crucial for the definitive diagnosis of benign myoepithelioma. A Ki67 index of 5–10% suggested a need for long-term surveillance. The postoperative course was uneventful with no recurrence at two years. This case highlights that myoepithelioma is a diagnostic chameleon and underscores the critical role of immunohistochemistry in achieving the correct diagnosis to guide appropriate management and follow-up.