a 52-year - old male had been treated for chronic renal failure and had been on continuous ambulatory peritoneal dialysis for 9 years . abdominopelvic computed tomography ( ct ) revealed a round mass in the lower pole of the left kidney and marked hydronephroureter with cortical thinning of bilateral kidneys ( fig . chest ct showed segmental consolidation with surrounding ground glass opacity in the right upper lobe , suggesting pulmonary tuberculosis . grossly , a well - circumscribed , round , solid mass measuring 2.52.01.5 cm was found at the lower pole of the left kidney . microscopically , most of the mass was composed of solid and thin tubules of eosinophilic oncocytic cells mixed with mature fat ( fig . the polygonal - shaped tumor cells had abundant eosinophilic granular cytoplasm and round nuclei with prominent nucleoli ( fig . the tumor demonstrated only focal large papillary fronds that contained delicate fibrovascular cores ( fig . 2e , right ) . occasionally , the oncocytic cells had mallory body  like eosinophilic cytoplasmic hyaline globules ( fig . immunohistochemically , both the oncocytic and clear cells were diffusely strongly positive for vimentin ( prediluted , v9 , dako , glostrup , denmark ) , pancytokeratin ( prediluted , ae1/ae3 , dako ) , and -methylacyl - coa racemase ( amacr ; 1:50 , epum1 , novocastra , new castle upon tyne , uk ) . some of the oncocytic cells were weakly positive for cd10 ( 1:100 , 56c6 , dako ) . the tumor cells were negative for epithelial membrane antigen ( prediluted , e29 , dako ) , cytokeratin 7 ( ck7 ; 1:100 , ov - tl , dako ) , moc31 ( moc31 ; 1:70 , novocastra ) , e - cadherin ( 1:50 , 36b5 , dako ) , carcinoembryonic antigen ( prediluted , dako ) , progesterone receptor ( 1:50 , pgr636 , dako ) , cd15 ( 1:50 , c3d-1 , dako ) , human melanoma black 45 ( hmb-45 ; prediluted , dako ) , transcription factor e3 ( 1:50 , mrq-37 , cell marque corporation , rocklin , ca , usa ) , and c - kit ( 1:30 , t595 , novocastra ) . these cells were also negative for hale s colloidal iron and periodic acid  schiff ( pas ) staining . mallory body  like eosinophilic hyaline globules were stained with pas and diastase - resistant ( fig . 2f , right ) , and they were slightly positive for cam 5.2 ( prediluted , bd bioscience , san diego , ca , usa ) and negative for -fetoprotein ( prediluted , dako ) . surrounding parenchyma as well as renal pelvis and ureter showed chronic granulomatous inflammation with caseation necrosis . electron microscopy revealed that the ovoid - shaped tumor cells had abundant cytoplasm and round nuclei with a euchromatic pattern . the mass was diagnosed as oncocytic rcc with a tubulopapillary growth pattern . during 9 years of postoperative institutional review board ( irb ) of gachon university gil medical center ( irb no . under light microscopy , the present renal tumor showed the characteristic pathologic findings of oncocytic tumor composed of mainly solid architecture with thin tubules , i.e. , short papillae and intermixed fat . there are several oncocytic renal cell neoplasms with these histopathological features , which poses a diagnostic problem in differentiation between rcc with oncocytic features , oncocytoma - like epithelioid angiomyolipoma ( aml ) , and renal oncocytoma . renal oncocytoma shows typical gross features of a solitary , well - circumscribed , slightly lobulated , solid appearance with a mahogany brown or dark red cut surface with a frequent central scar . microscopically , the small , round , uniform tumor cells of oncocytoma have abundant , faintly eosinophilic granular cytoplasm , and the cells are arranged in nests and tubulocystic , solid , or trabecular patterns with a myxomatous or hyalinized stroma . immunohistochemistry can be helpful for arriving at the correct diagnosis because the distinct immunopositivity for c - kit and the immunonegativity for ck7 and vimentin are characteristic of renal oncocytoma . clear cell rcc has diverse architecture of solid , alveolar , and acinar patterns , but prominent papillary architecture is not common . a focal tubular growth pattern with small papillae may be also seen in papillary rcc , but extensive tubular structures with intraluminal papillary projections have been rarely described . recent studies reported that a variant of oncocytic rcc having papillotubular growth shows the histology of an extensive small tubular growth pattern , often with papillary fronds . such tumors are mainly composed of oncocytic cells with eosinophilic granular cytoplasm and some scattered clear vacuolar cells [ 2 - 4 ] . either the oncocytic cells or the clear cells in those studies were positive for amacr , cd10 , ck7 , epithelial membrane antigen , and vimentin , but they were negative for c - kit and e - cadherin . these histological and immunohistochemical findings are partly shared by those of the present case . yet in the present case , the microscopic presence of mature fat among the monotonous polygonal cells with oncocytic cytoplasm suggested a possible diagnosis of oncocytoma - like epithelioid aml . epithelioid aml was often misdiagnosed as granular , chromophobe , or high - grade unclassified rcc until it was included in the classification system of renal tumors . therefore , this uncommonly encountered histologic feature should be distinguished from perinephric and sinus fat invasion of rcc . negative reaction for melanoma markers , such as hmb-45 , melan - a , microphthalmia transcription factor , and tyrosinase , and immunopositivity for such rcc markers as cd10 and epithelial membrane antigen , can exclude oncocytoma - like epithelioid aml . the present immunohistochemical results matched those of the tumor cells of papillary rcc and partly matched those of the oncocytic cells of papillary rcc showing papillotubular growth , as reported by masuzawa et al . recent molecular studies that have focused on oncocytic papillary rcc have revealed similar results to those of traditional papillary rcc showing frequent trisomies 7 , 12 , 16 , 17 , and 20 . park et al .   demonstrated that comparative genomic hybridization showed gains of 3p22 and 11q12-q13 in addition to chromosome 17 or loss of 4q . they also demonstrated a loss of chromosome 4 in one case of oncocytic papillary rcc . these molecular changes of oncocytic papillary rcc are similar to other types of papillary rcc . the mallory body  like eosinophilic hyaline globules are not commonly encountered in rcc , but they were first reported by datta in 1977 . these structures are morphologically similar to those seen in alcoholic liver disease , which is composed of a parallel array or granular aggregates of intermediate filaments . these prekeratin - like structures show similar immunohistochemical and special staining results as the present case . the present tumor arose in the background of tuberculous kidney . to date , less than 50 cases of rcc with renal tuberculosis have been reported . establishing a causative relationship between the chronic inflammation of tuberculosis and rcc is rather complicated , especially since we know from previous literature that bacillus calmette gurin interaction with the uroepithelium upregulates interleukins and various forms of interferon , which are currently the primary immunotherapies for rcc . we emphasize a rare morphology of oncocytic rcc with tubulopapillary growth pattern containing a mature fat component . this combination of pathologic findings are rarely encountered and should be distinguished from other types of rcc as well as oncocytoma - like epithelioid aml .