A rare case of exclusively oncocytic mucoepidermoid carcinoma with MAML2 translocation

Abstract

Mucoepidermoid carcinoma is the most common malignant tumor of the salivary gland. The oncocytic variant of mucoepidermoid carcinoma (OMEC) is rare and a small subset shows exclusive oncocytic morphology. Here we report an OMEC case of the parotid gland in a 74-year-old woman with exclusive oncocytes and rare mucocytes. The oncocytes showed diffuse nuclear positivity with p63 immunostaining. The MAML2 translocation was present, supporting the diagnosis of OMEC. Distinguishing OMEC with exclusive oncocytes from oncocytoma and oncocytic carcinoma can be very challenging for pathologists and is critical for proper clinical management. Our experience suggests that appropriate ancillary studies, especially the MAML2 translocation, may provide the essential evidence in difficult cases. Our literature review shows that the presence of mucocytes in an oncocytic neoplasm might be an important morphologic clue of OMEC. in the distinction of OMEC from other oncocytic neoplasms. We report an OMEC case of the left parotid gland in a 74-year-old woman. The neoplasm was composed exclusively of oncocytic cells and rare mucocytes. Fluorescence in situ hybridization (FISH) detected the MAML2 rearrangement in 44.5% of the tumor cells. Our case highlights the diagnostic challenge in OMEC with exclusive oncocytic morphology and the importance of utilizing appropriate ancillary studies in difficult cases. A literature review of previously reported OMEC cases with exclusive oncocytic morphology is also provided.