Malignant myoepithelial carcinoma of the parotid gland metastasizing to the lungs

A patient presented with a parotid mass, initially diagnosed as a pleomorphic adenoma following a superficial parotidectomy. Several months later the patient presented with dyspnoea, a right pleural effusion and extensive metastases to the lung and pleura. The subsequent pleural biopsy revealed a spindle cell tumour. Immunohistochemical staining did not support either a mesothelioma or spindle cell carcinoma. Staining for S100 protein and smooth muscle actin were positive, indicating these cells were myoepithelial in origin. Review of the previous parotid histology revealed that there were spindle-shaped cells within the initial parotid biopsy exhibiting pleomorphism and mitoses, with a similar morphological and immunohistochemical profile to cells within the pleural tumour. The initial parotid tumour was reclassified as a myoepithelial carcinoma. Further screening of the patient following this diagnosis revealed a recurrent parotid swelling: a neck dissection confirmed a malignant myoepithelial carcinoma. Careful screening of a pleomorphic adenoma and knowledge of a myoepithelial carcinoma is essential to prevent underdiagnosis of a malignant neoplasm.