Mucinous myoepithelioma: A report of a new variant.

Myoepitheliomas account for approximately 1.5% of all salivary gland tumors and arise most frequently from the parotid gland. Recently, a new myoepithelioma variant, called mucinous myoepithelioma, has attracted widespread attention. These tumors are recognized as a unique subtype of myoepithelioma, characterized by the presence of abundant mucin. We herein report the findings of an 86-year-old Japanese woman who presented with a hard mass of the right parotid gland behind her right ear which was gradually increasing in size. The patient had undergone a fine-needle aspiration biopsy 4 years earlier, and a cytological evaluation of a biopsy specimen had shown features of pleomorphic adenoma. A resection was thus performed and the tissue was found to be an encapsulated, soft and solid mass, and the cut surface was observed to be a capsulated and well-defined tumor lesion with myxoid-looking foci of gray-white coloration. Microscopic examination revealed that this lesion was composed of a proliferation of bland-looking epithelial and myoepithelial cells, arranged in a solid or reticular growth fashion in an abundant myxomatous or hyalinized stroma. These neoplastic epithelial cells had centrally located small nuclei with fine chromatin and abundant clear to eosinophilic cytoplasm, often containing mucin in a uniform pattern. Immunohistochemical staining demonstrated the tumor cells to be positive for AE1/AE3, S-100 and mucicarmine. Our findings suggest this case to be one myoepithelioma variant of mucinous myoepithelioma, and more experience related to this myoepithelioma variant is necessary to better understand its biological behavior and make an accurate diagnosis for a proper treatment.