Oncocytic mucoepidermoid carcinoma of the parotid gland with CRTC1-MAML2 fusion transcript: report of a case with review of literature.

Oncocytic mucoepidermoid carcinoma is a very rare variant of mucoepidermoid carcinoma, composed predominantly of oncocytic cells. Most previously reported cases described the difficulty in histologic differentiation from other oncocytic tumors. Here we report a case of oncocytic mucoepidermoid carcinoma of parotid gland diagnosed by the detection of CRTC1-MAML2 fusion. A 53-year-old man had a left superficial parotidectomy conducted for 3-cm-sized mass. The resected tumor was composed almost exclusively of oncocytic tumor cells. With detailed histologic evaluation, scarce vacuolated tumor cells, suggestive of mucous cell of mucoepidermoid carcinoma, and one focus of tumor embolism in a vein were found, suggesting the possibility of oncocytic mucoepidermoid carcinoma. Immunohistochemically, oncocytic cells were diffusely positive for p63. Reverse transcriptase polymerase chain reaction and direct sequencing revealed CRTC1-MAML2 translocation of this tumor. To our knowledge, this report describes the first case of oncocytic mucoepidermoid carcinoma confirmed with CRTC1-MAML2 fusion. Identification of this fusion gene may help in distinguishing oncocytic mucoepidermoid carcinoma from its mimics.