a 71-year - old man presented with a four - year history of a right infra - auricular mass . head and neck computed tomography revealed a mass with heterogenous density and a fatty component ( fig . partial parotidectomy was performed , revealing a solitary well - defined mass measuring 4.23.52.5 cm with a thin capsule . the tumor comprised oncocytic cells and fat cells with mature adipose tissue occupying about 50% to 60% of the tumor . immunohistochemically , the oncocytic cells were strongly positive for ae1/ae3 ( 1:1,000 , dako , glostrup , denmark ) and cytokeratin 7 ( 1:1,000 , dako ) . peripheral cells were stained by p63 ( 1:1,000 , dako ) and cytokeratin 5/6 ( 1:200 , dako ) . epithelial membrane antigen ( 1:200 , dako ) stained the luminal surface and sebaceous glands . the oncocytic cells were negative for smooth muscle actin ( 1:1,000 , dako ) and calponin ( 1:1,000 , dako ) . cytokeratin 14 ( 1:400 , biogenex , the hague , the netherlands ) expression was restricted to sites of sebaceous differentiation . an apical - luminal pattern of dog1 ( 1:200 , leica , newcastle upon tyne , uk ) staining was observed in the normal serous acini , while the tumor cells were negative ( fig . 2c , d ) . based on the microscopic findings , we rendered a diagnosis of oncocytic lipoadenoma with sebaceous differentiation . this rare tumor was not mentioned as an entity in the 2005 world health organization ( who ) histologic classification of tumors of salivary glands . in the english literature , there is no gender predilection , and the patient ages range from 7 to 89 years ( median of 55.5 years ) . the universal microscopic finding in the literature was an encapsulated tumor comprising a mixture of oncocytic cells and fat cells . uncommon findings as sclerotic and polycystic changes ascribed to chronic involution , squamous metaplasia , lymphoid stroma , and metaplastic bone formation have been reported . the presence of mitochondria in those oncocytic cells was confirmed by both immunohistochemical and ultrastructural studies . phosphotungstic acid hematoxylin staining and antimitochondrial antibody were utilized to demonstrate the presence of mitochondria [ 3,6 - 8 ] . ultrastructural studies also provided evidence that oncocytic lipoadenoma may be derived from striated ductal cells based on similar histological features . dog1 expression was found in both normal and neoplastic counterparts of intercalated ducts and acinar cells , whereas striated duct cells were negative . the oncocytic cells in our case were negative for dog1 , which supports the contention that striated ductal cells were the origin of this tumor . differential diagnoses include sialolipoma , oncocytoma , oncocytosis , sclerosing polycystic adenosis , and oncocytic metaplasia . oncocytomas are also encapsulated tumors with immunohistochemical findings identical to those of oncocytic lipoadenomas , but they lack adipose tissue as their component cells . in addition , 20% of patients with oncocytomas have a history of radiation exposure . the presence of sclerotic and polycystic change can be reminiscent of sclerosing polycystic adenosis , but oncocytic lipoadenomas lack xanthomatous and apocrine change , which is commonly seen in sclerosing polycystic adenosis . in addition , the presence of acini in sclerosing polycystic adenosis can be aided by dog1 antibody . sebaceous differentiation is not an uncommon finding in salivary glands and can be found in sebaceous lymphadenoma , sebaceous adenoma , pleomorphic adenoma , oncocytoma , sialoblastoma , and warthin tumor . the majority of the reported oncocytic lipoadenomas including our case exhibit sebaceous differentiation . lipoadenomas are similar to adenolipomas of the breast , thyroid , and skin in that they all demonstrate a histological mixture of epithelial components and adipose tissue . in contrast to adenolipoma , which is considered to be a hamartoma , oncocytic lipoadenoma is believed to be a true neoplasm . an altered hmga2 gene rearrangement is more commonly seen in lipoma , pleomorphic adenoma , and leiomyoma .
oncocytic lipoadenoma is a rare tumor , with only 18 cases having been reported since the first in 1998 . 
 we encountered a case of oncocytic lipoadenoma presenting as a slowly growing parotid mass in a 71-year - old man . 
 this tumor is characteristically comprised of a mixture of oncocytes and adipocytes . 
 the present case is one of five reported cases of oncocytic lipoadenoma showing sebaceous differentiation . 
 the results of immunohistochemical study with dog1 antibody supported the origination of this tumor in the striated duct .