A Case Series of a Rare Parotid Gland Oncocytic Mucoepidermoid Carcinoma

Abstract Introduction/Objective We analyzed two cases of oncocytic mucoepidermoid carcinoma (OMEC) of the parotid gland which highlight the diagnostic challenges of oncocytic salivary gland neoplasms. OMEC’s are a rare type of salivary gland tumor commonly arising from the parotid gland that can easily be mistaken as benign. Proper pathologic diagnosis of these masses is critical, as it guides therapeutic intervention and has prognostic significance. Methods/Case Report In this case series, two patients were analyzed retrospectively for unilateral parotid masses. Results (if a Case Study enter NA) In a 67-year-old female, an MRI and biopsy were performed. Only a differential diagnosis could be provided, which favored oncocytoma or oncocytic carcinoma. Due to this uncertainty, a complete excision of the mass was performed. Considering the cytomorphology, immunohistochemistry (CK5/6 and P63 in oncocytes), and mucicarmine special stain highlighting scattered mucocytes, the patient was diagnosed with a low- grade OMEC. In our second case, an 80-year-old female, FNA of a posterior left ear mass 1 year prior revealed a low- grade oncocytic proliferation. With the presence of a left parotid mass one year later, additional imaging was performed and showed increased T2 hyperintensity on MRI, which caused concern for the clinicians. A superficial limited parotidectomy was performed and a differential of oncocytoma versus oncocytic variant of mucoepidermoid carcinoma was rendered. Further tumor characterization with fluorescence in situ hybridization (FISH) demonstrated a MAML2 translocation which guided diagnosis of OMEC. Conclusion With approximately 30% of all malignant salivary gland tumors being constituted by mucoepidermoid carcinoma, the ability to accurately diagnose even this rare subtype, oncocytic mucoepidermoid carcinoma, is of significant importance and relevance to pathologists in many practice settings. Herein we demonstrate the utility of H&E morphology, immunohistochemistry, and MAML2 FISH in diagnosing OMEC in the setting of oncocytic salivary gland lesions. Future avenues, including tumor molecular profiling, will aid in elucidating clinicopathologic characteristics of this entity.