renal neoplasms are composed of heterogeneous groups including clear cell renal cell carcinoma ( rcc ) , papillary rcc , chromophobe rcc , collecting duct carcinoma , oncocytoma , and others . in most cases , these categories are easily differentiated from each other on the basis of histologic features alone . occasionally , however , there are overlapping morphological characteristics between such tumors as well as histologic heterogeneity within a single tumor . in those cases these two types of tumors have a common origin , distal nephrons , and similar phenotype , so it may be difficult to distinguish these tumors in the practice of diagnostic pathology . chromophobe rcc and oncocytoma should be distinguished from each other because both tumors have different behaviors and clinical outcomes . oncocytoma is a benign tumor , whereas chromophobe rcc is a subtype of rcc , namely , malignant . in recent years , several studies have been carried out to find helpful ancillary means to distinguish chromophobe rcc from oncocytoma . however , the results of these studies are inconsistent and still unsatisfactory [ 1 - 8 ] . caveolin-1 , a 24-kd membrane protein , is a major structural and functional protein component of caveolae , endocytic structures of the cell membrane . several studies have shown that the expression of caveolin-1 is elevated in various types of malignancies such as prostate , breast , colon , esophagus , and urinary bladder cancers [ 11 - 14 ] , but the precise roles of caveolin-1 in carcinogenesis are still unclear . moc-31 is a kind of cell surface glycoprotein and is expressed in most benign and malignant epithelia . it is known that moc-31 is useful for distinguishing adenocarcinoma from mesothelioma as well as hepatocellular carcinoma from cholangiocarcinoma and metastatic adenocarcinoma in the liver . in this study , we intended to identify whether there were any differences in immunohistochemical reactivity for caveolin-1 and moc-31 between chromophobe rcc and oncocytoma and to determine whether the expression of these proteins has a benefit as useful immunohistochemical markers in distinguishing the tumors . in addition , clear cell rcc , particularly the granular cell type , may also have a phenotype similar to the previously mentioned two types of tumors and cause a diagnostic problem . accordingly , we also investigated the immunohistochemical reactivity of clear cell rcc for caveolin-1 and moc-31 and evaluated the differences among clear cell rcc , chromophobe rcc , and oncocytoma . twenty - three chromophobe rccs and 8 oncocytomas were retrieved from the surgical pathology archives between 1997 and 2006 at three institutes . twenty - five clear cell rccs , including 10 cases of clear cell type and 15 cases of granular cell type , were also selected from the surgical pathology files of one institute . two pathologists , one of whom has expertise in genitourinary pathology , reviewed all cases and achieved consensus on classification according to the recommendations of the international union against cancer   and the world health organization classification of tumors . electron microscopic examination was performed for 9 cases because they showed obscure and overlapping histologic features on light microscopic , histochemical , and immunohistochemical examinations . two cases having unclear features despite the electron microscopic examination were excluded from this study . staging of chromophobe rcc was performed according to the recently updated staging system ( 7th edition ) of the american joint committee on cancer ( ajcc ) ( 7th edition ) and the union internationale contre le cancer ( uicc ) . the immunohistochemical staining was performed with the dako envision kit ( dako , denmark ) on sections prepared from formalin - fixed and paraffin - embedded specimens that were dewaxed and rehydrated with graded concentrations of alcohol . endogenous peroxidase was blocked by dipping the sections in 3% aqueous hydrogen peroxide for 10 min , and antigen retrieval was performed with a 10-min microwave treatment in 10 mmol / l citrate buffer , ph 6.0 . for immunohistochemical staining of moc-31 , target retrieval solution ( dako , denmark ) diluted primary antibodies for caveolin-1 ( 1:200 , transduction laboratories , us ) and moc-31 ( 1:50 , dako , denmark ) were treated at room temperature for 30 min and 1 h , respectively . after the primary antibody incubation , the sections were incubated with the secondary antibody . immunoreactivity for caveolin-1 and moc-31 was considered as diffuse positive when 50% or more of the tumor cells were stained , as focal positive when 10% to 49% of the tumor cells were stained , and as negative when less than 10% of the tumor cells were stained . internal positive controls were endothelial cells and distal tubular epithelial cells for caveolin-1 and moc-31 , respectively . chicago , il , usa ) to evaluate correlation between the tumor types and expression of immunohistochemical stain for caveolin-1 and moc-31 . twenty - three chromophobe rccs and 8 oncocytomas were retrieved from the surgical pathology archives between 1997 and 2006 at three institutes . twenty - five clear cell rccs , including 10 cases of clear cell type and 15 cases of granular cell type , were also selected from the surgical pathology files of one institute . two pathologists , one of whom has expertise in genitourinary pathology , reviewed all cases and achieved consensus on classification according to the recommendations of the international union against cancer   and the world health organization classification of tumors . electron microscopic examination was performed for 9 cases because they showed obscure and overlapping histologic features on light microscopic , histochemical , and immunohistochemical examinations . two cases having unclear features despite the electron microscopic examination were excluded from this study . staging of chromophobe rcc was performed according to the recently updated staging system ( 7th edition ) of the american joint committee on cancer ( ajcc ) ( 7th edition ) and the union internationale contre le cancer ( uicc ) . the immunohistochemical staining was performed with the dako envision kit ( dako , denmark ) on sections prepared from formalin - fixed and paraffin - embedded specimens that were dewaxed and rehydrated with graded concentrations of alcohol . endogenous peroxidase was blocked by dipping the sections in 3% aqueous hydrogen peroxide for 10 min , and antigen retrieval was performed with a 10-min microwave treatment in 10 mmol / l citrate buffer , ph 6.0 . for immunohistochemical staining of moc-31 , target retrieval solution ( dako , denmark ) was used for antigen retrieval . diluted primary antibodies for caveolin-1 ( 1:200 , transduction laboratories , us ) and moc-31 ( 1:50 , dako , denmark ) were treated at room temperature for 30 min and 1 h , respectively . immunoreactivity for caveolin-1 and moc-31 was considered as diffuse positive when 50% or more of the tumor cells were stained , as focal positive when 10% to 49% of the tumor cells were stained , and as negative when less than 10% of the tumor cells were stained . internal positive controls were endothelial cells and distal tubular epithelial cells for caveolin-1 and moc-31 , respectively . chicago , il , usa ) to evaluate correlation between the tumor types and expression of immunohistochemical stain for caveolin-1 and moc-31 . in normal kidney tissue , expression of caveolin-1 was seen in parietal epithelia of bowman capsules , endothelial cells , and smooth muscle cells of blood vessels but not in endothelial cells of glomeruli or any other epithelia ( table 2 , fig . 1a ) . in chromophobe rccs , 20 ( 87% ) of 23 cases showed diffuse positivity for caveolin-1 . all positive cases showed expression of caveolin-1 in 90% or more of the tumor cells and moderate to strong intensity except for one case that had relatively weak intensity . in most of the cases , the cell membrane was also stained and the staining intensity was stronger in the membrane than in the cytoplasm ( fig . 2a ) . in the three negative cases , none of the tumor cells expressed caveolin-1 . 2b ) . none of the tumor cells expressed caveolin-1 except for one case in which caveolin-1 was expressed in only 5% or less of the tumor cells . clear cell rccs were diffuse positive in 19 , focal positive in 2 , and negative in 4 . the total number of positive cases was 21 ( 84% ) of 25 clear cell rccs . all 10 cases of the clear cell type were diffuse positive , whereas 9 ( 60% ) of 15 cases of the granular cell type were diffuse positive . there was a slight difference in the pattern of immunohistochemical staining between the clear and granular cell types . all cases of the clear cell type showed dominantly membranous staining without cytoplasmic staining ( fig . 3a ) , whereas most cases of the granular cell type exhibited a similar staining pattern to that of chromophobe rcc , namely , a diffusely cytoplasmic and granular pattern with focal membranous condensation ( fig . the incidence of caveolin-1 expression showed statistically significant differences between chromophobe rccs and oncocytomas ( p<0.001 ) and between clear cell rccs and oncocytomas ( p<0.001 ) but not between chromophobe and clear cell rccs ( p=0.466 ) ( table 3 , 4 ) . moc-31 was positive in distal tubules and collecting ducts of normal kidney tissue but negative in other epithelial and mesenchymal tissues ( table 2 , fig . moc-31 was diffuse positive in 22 ( 96% ) of 23 chromophobe rccs , showing a strong membranous pattern of immunohistochemical staining ( fig . moc-31 was negative in 6 of 8 cases and diffuse positive in the other 2 cases ( 25% ) ( fig . three of the six negative cases expressed moc-31 in less than 10% of the tumor cells , and the other three cases showed no staining . in the former three cases , moc-31 was characteristically expressed in the tumor cells showing tubular structures but not solid nests or trabecular structures . in addition , two oncocytomas showing diffuse expression of moc-31 were composed of predominantly tubular structures , and solid or trabecular structures were only a minor portion . moc-31 was expressed in such tubular structures rather than in solid or trabecular structures ( fig . clear cell rccs were diffuse positive for moc-31 in 12 , focal positive in 2 , and negative in 11 . in particular , the granular cell type of clear cell rcc showed less positivity for moc-31 than did the clear cell type . only 6 ( 40% ) of 15 cases of the granular cell type were positive for moc-31 . the incidence of moc-31 expression showed statistically significant differences between chromophobe rccs and oncocytomas ( p<0.001 ) and between chromophobe and clear cell rccs ( p<0.001 ) but not between clear cell rccs and oncocytomas ( p=0.215 ) ( table 3 , 4 ) . in normal kidney tissue , expression of caveolin-1 was seen in parietal epithelia of bowman capsules , endothelial cells , and smooth muscle cells of blood vessels but not in endothelial cells of glomeruli or any other epithelia ( table 2 , fig . 1a ) . in chromophobe rccs , 20 ( 87% ) of 23 cases showed diffuse positivity for caveolin-1 . all positive cases showed expression of caveolin-1 in 90% or more of the tumor cells and moderate to strong intensity except for one case that had relatively weak intensity . in most of the cases , the cell membrane was also stained and the staining intensity was stronger in the membrane than in the cytoplasm ( fig . 2a ) . in the three negative cases , none of the tumor cells expressed caveolin-1 . 2b ) . none of the tumor cells expressed caveolin-1 except for one case in which caveolin-1 was expressed in only 5% or less of the tumor cells . clear cell rccs were diffuse positive in 19 , focal positive in 2 , and negative in 4 . the total number of positive cases was 21 ( 84% ) of 25 clear cell rccs . all 10 cases of the clear cell type were diffuse positive , whereas 9 ( 60% ) of 15 cases of the granular cell type were diffuse positive . there was a slight difference in the pattern of immunohistochemical staining between the clear and granular cell types . all cases of the clear cell type showed dominantly membranous staining without cytoplasmic staining ( fig . 3a ) , whereas most cases of the granular cell type exhibited a similar staining pattern to that of chromophobe rcc , namely , a diffusely cytoplasmic and granular pattern with focal membranous condensation ( fig . the incidence of caveolin-1 expression showed statistically significant differences between chromophobe rccs and oncocytomas ( p<0.001 ) and between clear cell rccs and oncocytomas ( p<0.001 ) but not between chromophobe and clear cell rccs ( p=0.466 ) ( table 3 , 4 ) . moc-31 was positive in distal tubules and collecting ducts of normal kidney tissue but negative in other epithelial and mesenchymal tissues ( table 2 , fig . moc-31 was diffuse positive in 22 ( 96% ) of 23 chromophobe rccs , showing a strong membranous pattern of immunohistochemical staining ( fig . moc-31 was negative in 6 of 8 cases and diffuse positive in the other 2 cases ( 25% ) ( fig . three of the six negative cases expressed moc-31 in less than 10% of the tumor cells , and the other three cases showed no staining . in the former three cases , moc-31 was characteristically expressed in the tumor cells showing tubular structures but not solid nests or trabecular structures . in addition , two oncocytomas showing diffuse expression of moc-31 were composed of predominantly tubular structures , and solid or trabecular structures were only a minor portion . moc-31 was expressed in such tubular structures rather than in solid or trabecular structures ( fig . clear cell rccs were diffuse positive for moc-31 in 12 , focal positive in 2 , and negative in 11 . in particular , the granular cell type of clear cell rcc showed less positivity for moc-31 than did the clear cell type . only 6 ( 40% ) of 15 cases of the granular cell type were positive for moc-31 . the incidence of moc-31 expression showed statistically significant differences between chromophobe rccs and oncocytomas ( p<0.001 ) and between chromophobe and clear cell rccs ( p<0.001 ) but not between clear cell rccs and oncocytomas ( p=0.215 ) ( table 3 , 4 ) . although each renal cell tumor has unique characteristics , they may occasionally have overlapping histologic features that make it difficult to make a proper diagnosis . chromophobe rcc consists of tumor cells showing abundant pale cytoplasm with a perinuclear halo and peripheral condensation and hyperchromatic , irregular , wrinkled nuclei . by contrast , oncocytomas have tumor cells showing abundant eosinophilic granular cytoplasm and regular and round nuclei . however , occasionally , when the tumors show obscure microscopic findings , it can be difficult to make a differential diagnosis . therefore , many investigators have searched for helpful ancillary means to discriminate these two types of renal tumors . electron microscopic examination is an important and useful tool in the differential diagnosis of chromophobe rcc and oncocytoma . however , electron microscopic examination is technically difficult , expensive , and not available in many laboratories . several studies have suggested that hale 's colloidal iron stain is helpful for the differential diagnosis of chromophobe rcc from oncocytoma . however , hale 's colloidal iron stain is also technically demanding and difficult to interpret , and therefore reproducibility is relatively low . several studies with various immunohistochemical markers , including kidney - specific cadherin , ck7 , ema , cd10 , parvalbumin , rcc , c - kit , and ron proto - oncogene , have been performed to find useful markers for distinguishing chromophobe rcc from oncocytoma . however , the results of these studies are inconsistent or turned out to be not satisfactory . accordingly , the use of these markers in differential diagnosis is limited [ 2 - 8,21,22 ] . caveolin-1 is a major protein component of caveolae , which are endocytic structures of the cell membrane , and is localized to the cytosolic surface of caveolae . caveolin-1 interacts with both lipids and lipid anchors on proteins ; therefore , it has multiple functions in signal transduction , membrane traffic , and intracellular and extracellular lipid transport . expression of this molecule has been studied in various types of tumors , including prostate , breast , colon , esophagus , and urinary bladder cancers [ 11 - 14 ] . however , only a small number of studies have recently reported a relationship between the expression of caveolin-1 and renal neoplasms , including chromophobe rcc and oncocytoma [ 23 - 25 ] . in the present study , caveolin-1 was expressed in 20 ( 87% ) of 23 chromophobe rccs but in 0 of 8 oncocytomas . all positive cases of chromophobe rcc showed diffuse , moderate to strong staining in 90% or more of tumor cells and cytoplasmic and granular staining with membranous condensation . this clear discrimination enables the use of caveolin-1 for differential diagnosis between chromophobe rcc and oncocytoma ( p<0.001 ) . carrion et al and mete et al reported that most oncocytomas express caveolin-1 with a diffuse cytoplasmic staining pattern and that chromophobe rccs show a relatively decreased expression of caveolin-1 . this difference probably originated from the artifact that they did not use a blocking step for endogenous biotin despite using an avidin - biotin peroxidase kit . nevertheless , there was a difference in staining pattern between chromophobe rccs and oncocytomas in their studies . according to them , there was an obvious difference in the incidence and staining pattern of caveolin-1 expression between both tumors . in contrast with these findings , garcia and li reported that caveolin-1 was positive in all 21 chromophobe rccs but was focal positive , with staining in less than 20% of the tumor cells , in only 3 of 26 oncocytomas . occasionally , it may also be difficult to distinguish clear cell rcc , particularly the granular cell type , from chromophobe rcc or oncocytoma in practice . twenty - one ( 84% ) of 25 clear cell rccs were positive for caveolin-1 , including 2 focal positive cases . granular cell type tumors of clear cell rccs were very similar to chromophobe rcc in staining pattern as well as extent , whereas clear cell type tumors differed from chromophobe rcc , that is , showing membranous staining . on the basis of these results , the granular cell type of clear cell rcc could be differentiated from oncocytoma ( p<0.001 ) but not chromophobe rcc ( p=0.466 ) . moc-31 , a kind of cell surface glycoprotein , is expressed in various benign and malignant epithelia , but its function is still unclear . moc-31 has been studied for differential diagnosis between hepatocellular carcinoma and cholangiocarcinoma or metastatic adenocarcinoma in the liver or between mesothelioma and adenocarcinoma . studies associated with renal neoplasms have rarely been performed . in our study , moc-31 showed diffuse , strong , and membranous staining in 22 ( 96% ) of 23 chromophobe rccs and diffuse cytoplasmic staining in only 2 ( 25% ) of 8 oncocytomas . the other six cases of oncocytomas were considered to be negative , but three of them expressed moc31 with cytoplasmic staining in less than 10% of the tumor cells . in these three cases and the diffuse positive two cases of oncocytomas , moc-31 was predominantly expressed in the tumor cells showing tubular differentiation rather than solid or trabecular structures . this seems to be related to the fact that moc-31 is expressed in distal tubular cells of normal kidney . although most oncocytomas do not express moc-31 , some oncocytomas may express moc-31 if they are differentiated toward tubules and have similar structural features to normal distal tubules . further molecular analysis is needed to uncover the precise function of moc-31 in tubular differentiation and tumorigenesis . according to our result for moc31 expression , diffuse membranous expression of moc-31 is a feature of chromophobe rcc rather than of oncocytoma , particularly not showing tubular differentiation ( p<0.001 ) . pan et al showed that 23 ( 82% ) of 28 chromophobe rccs were positive for moc-31 , whereas all 7 oncocytomas were completely negative . clear cell rccs expressed moc-31 in 14 ( 56% ) of 25 cases , including 2 focal positive cases . considering only the granular cell type , as previously mentioned , clear cell rcc had a statistically significant difference in the expression of moc-31 from chromophobe rcc ( p<0.001 ) but not oncocytoma ( p=0.215 ) . for example , if a tumor is negative for moc-31 , it is more likely to be clear cell rcc than chromophobe rcc . the results of the present study showed an obvious discrimination between chromophobe rcc and oncocytoma in the expression of caveolin-1 and moc-31 . in other words , these immunohistochemical markers are thought to be considerably useful for distinguishing these tumors . in addition , clear cell rcc also showed a different expression of caveolin-1 and moc-31 from oncocytoma and chromophobe rcc , respectively . if used together with other known markers such as c - kit or rcc marker , both caveolin-1 and moc-31 may be helpful in the differentiation of clear cell rcc from chromophobe rcc or oncocytoma .
purposerenal tumors consist of heterogeneous groups that frequently show complex and overlapping morphology , thus making it difficult to make a correct diagnosis . 
 one of the most problematic differential diagnoses is to distinguish chromophobe renal cell carcinoma ( rcc ) from oncocytoma . 
 these should be distinguished by differences in their behavior and clinical outcome . 
 our study was performed to identify whether caveolin-1 and moc-31 are useful immunohistochemical markers for differentiating chromophobe rcc from oncocytoma.materials and methodswe selected 23 chromophobe rccs , 8 oncocytomas , and 25 clear cell rccs and performed immunohistochemical staining for caveolin-1 and moc-31.resultscaveolin-1 was positive in 20 ( 87% ) of 23 chromophobe rccs , 0 of 8 oncocytomas , and 21 ( 84% ) of 25 clear cell rccs . 
 moc-31 was positive in 22 ( 96% ) of 23 chromophobe rccs , 2 ( 25% ) of 8 oncocytomas , and 14 ( 56% ) of 25 clear cell rccs . 
 there was a statistically significant difference in the expression of caveolin-1 and moc-31 between chromophobe rcc and oncocytoma ( p<0.001 ) . 
 in addition , clear cell rcc was also significantly different from oncocytoma in the expression of caveolin-1 ( p<0.001 ) and was significantly different from chromophobe rcc in the expression of moc-31 ( p<0.001).conclusionscaveolin-1 and moc-31 can be useful markers in the differential diagnosis of chromophobe rcc , oncocytoma , and clear cell rcc .