A case of submucosal buccal oncocytoma in a patient with Birt-Hogg-Dubé syndrome

Birt-Hogg-Dub syndrome (BHDS) is caused by mutations of the folliculin (FLCN) tumor suppressor gene.BHDS is a triad of skin tumors, multiple lung cysts or pneumothorax, and renal tumors.Some patients with BHDS can develop oncocytoma.We report a case of oncocytoma in the minor salivary gland of the buccal mucosa of a patient with BHDS.A 69-year-old man visited our hospital with a complaint of a mass on the left buccal submucosa.The 1510 mm mass was painless and slightly soft in elasticity.Although the mass was well demarcated on magnetic resonance imaging, the signal intensity of the mass was heterogeneous.The histopathological diagnosis of a biopsy specimen was oncocytoma or oncocytic hyperplasia.Accordingly, the mass was extirpated under local anesthesia.Histopathological examination revealed sheets of large polyhedral cells, oncocytes, with abundant granular, eosinophilic cytoplasm.Based on the histopathological features, the final diagnosis was oncocytoma.No recurrence was observed 11 months postoperatively.Genetic analysis of the oncocytoma revealed germline, but not somatic, mutation in FLCN.The findings highlight the importance of the role of FLCN in tumorigenesis to clarify the mechanism of oncocytoma development in the salivary glands of BHDS patients.