Pleomorphic adenoma with bizarre myoepithelial cells: A diagnostic challenge on cytologic smear

The diagnosis on fine needle aspiration of salivary gland tumors with a myoepithelial component is challenging because myoepithelial cells can have a wide cytomorphologic spectrum. The authors report a case of a pleomorphic adenoma of the parotid gland that expands the spectrum of appearances that myoepithelial cells can show with this tumor. A 55-year-old female was found to have a right parotid gland mass. FNA showed hypercellularity, with loosely cohesive fragments of spindle-shaped myoepithelial cells admixed with small nests of epithelial cells. Interspersed may occasional bizarre cells possessing severely pleomorphic nuclei with hyperchromasia. The cytologic diagnosis was "suspicious for carcinoma ex pleomorphic adenoma." A total parotidectomy was performed with complete resection of the tumor that was confirmed to be a pleomorphic adenoma. The pleomorphic cells noted on FNA were scattered throughout the tumor, and were positive by immunostaining for keratin, S-100 protein and p63, identifying them as myoepithelial cells. These cells did not show mitotic activity and were negative for Ki67. The pleomorphic adenoma showed extensive degenerative changes including central cyst formation, stromal hyalinization and hemosiderin deposition. On the basis of the combined light microscopic and immunohistochemical findings, there was no evidence to support a malignant change in the pleomorphic adenoma. It was concluded the pleomorphic myoepithelial cells were a degenerative change, reminiscent of what is seen in "ancient" schwannoma and some uterine leiomyomata. Our case expands the spectrum of appearances that can be seen in myoepithelial cells in the salivary gland.