Renal oncocytoma: II. Lectin and immunohistochemical features indicating an origin from the collecting duct

Immunohistochemistry of Complement Response on Human Renal Cell Carcinoma Biopsies

The goal of the study was to characterize the complement humoral and cellular antitumor responses on primary renal cell carcinoma biopsies. As an original observation, complement activation was found on 11/22 cases. Classical complement pathway activation was characterized by tumor C1q complement protein and IgG deposition (5/22 cases). Alternative or nonimmune complement pathway activation was seen as tissue deposition of C3 (6/22 cases). The membrane attack complex was present in cases with alternative complement pathway activation at the sites of tumor necrosis. Renal cell carcinomas with complement activation overexpressed at least one of the complement regulatory factors (membrane cofactor protein, decay accelerating factor, membrane attack complex inhibitor) and major histocompatibility complex class II molecules. Tumor infiltrating lymphocytes were present in most of the renal cell carcinomas with complement activation (8/11). However, the number of tumor-infiltrating lymphocytes was correlated with the intensity of major histocompatibility complex-ll expression in 18/22 cases. Detection of complement activation and immune cell infiltrates on renal cell carcinoma primary biopsies may serve as a new predictive factor for immunotherapy.

Immune signature of tumor infiltrating immune cells in renal cancer

Tumor-associated immune cells have been discussed as an essential factor for the prediction of the outcome of tumor patients. Lymphocyte-specific genes are associated with a favorable prognosis in colorectal cancer but with poor survival in renal cell carcinoma (RCC). Flow cytometric analyses combined with immunohistochemistry were performed to study the phenotypic profiles of tumor infiltrating lymphocytes (TIL) and the frequency of T cells and macrophages in RCC lesions. Data were correlated with clinicopathological parameters and survival of patients. Comparing oncocytoma and clear cell (cc)RCC, T cell numbers as well as activation-associated T cell markers were higher in ccRCC, whereas the frequency of NK cells was higher in oncocytoma. An intratumoral increase of T cell numbers was found with higher tumor grades (G1:G2:G3/4 = 1:3:4). Tumor-associated macrophages slightly increased with dedifferentiation, although the macrophage-to-T cell ratio was highest in G1 tumor lesions. A high expression of CD57 was found in T cells of early tumor grades, whereas T cells in dedifferentiated RCC lesions expressed higher levels of CD69 and CTLA4. TIL composition did not differ between older (>70 y) and younger (<58 y) patients. Enhanced patients' survival was associated with a higher percentage of tumor infiltrating NK cells and Th1 markers, e.g. HLA-DR+ and CXCR3+ T cells, whereas a high number of T cells, especially with high CD69 expression correlated with a worse prognosis of patients. Our results suggest that immunomonitoring of RCC patients might represent a useful tool for the prediction of the outcome of RCC patients.

An overview of renal cell cancer: pathology and genetics

Renal cell carcinoma is a group of malignancies arising from the epithelium of the renal tubules. The pattern of somatic mutations in kidney tumors has been extensively investigated. In the current 2004 WHO classification, the molecular background of a renal tumor has become, in addition to histopathology, a major criterion for tumor classification. The goal of this review is to discuss morphology and genetics of adult renal epithelial cancer included in the 2004 WHO classification and to mention renal tumor types, which are not considered in the current WHO classification. Further, pathologic considerations with clinical and prognostic implications are provided.

Claudin-7 immunohistochemistry in renal tumors: a candidate marker for chromophobe renal cell carcinoma identified by gene expression profiling

CONTEXT

The differential diagnosis of eosinophilic renal tumors can be difficult by light microscopy. In particular, chromophobe renal cell carcinoma (RCC) is difficult to distinguish from oncocytoma. This differential diagnosis is important because chromophobe RCC is malignant, whereas oncocytoma is benign. Furthermore, chromophobe RCC has distinct malignant potential and prognosis compared with eosinophilic variants of other RCC subtypes. Immunohistochemistry is useful for distinguishing chromophobe RCC from other subtypes of renal carcinoma, but no expression marker reliably separates chromophobe RCC from oncocytoma.

OBJECTIVE

In a previous gene expression microarray analysis of renal tumor subtypes, we found the distal nephron markers claudin-7 and claudin-8 to be overexpressed in chromophobe RCC versus oncocytoma and other tumor subtypes. We have confirmed similar findings in independent microarray data and validated differential claudin-7 protein expression by immunohistochemistry.

DESIGN

Immunohistochemical analysis of claudin-7 in 36 chromophobe RCCs, 43 oncocytomas, 42 clear cell RCCs, and 29 papillary RCCs.

RESULTS

Membranous claudin-7 expression was detected in 67% chromophobe RCCs, compared with 0% clear cell RCCs, 28% papillary RCCs, and 26% oncocytomas (P < .001).

CONCLUSIONS

Based on microarray and immunohistochemical data, we propose claudin-7 to be a candidate expression marker for distinguishing chromophobe RCC from other renal tumor subtypes, including the morphologically similar oncocytoma. The clinical utility of claudin-7 should be validated in independent studies of renal tumors, possibly in combination with additional targets in a multiplex immunohistochemical panel.

ARPP protein is selectively expressed in renal oncocytoma, but rarely in renal cell carcinomas

We have recently isolated a gene, Ankyrin-repeated protein with a proline-rich region (ARPP), that is highly expressed in the skeletal and cardiac muscle. Our previous immunohistochemical analysis revealed that ARPP expression was augmented in rhabdomyosarcoma but scarcely detectable in leiomyosarcoma, showing that ARPP is a useful marker for rhabdomyosarcoma. In the present study, we generated the anti-ARPP monoclonal antibody, YAS11, immunoreactive with the N-terminal region (amino-acids residues 1-145) of the ARPP protein. Further, we immunohistochemically analyzed 100 renal tumors including 14 oncocytomas, and 86 renal cell carcinomas (RCCs). We found that ARPP was highly expressed in 12 of the 14 (85.7%) oncocytomas, but was detectable in only four of the 86 (4.7%) RCCs. Interestingly, ARPP was not detected in any of 11 chromophobe RCCs, suggesting that ARPP may be useful for differential diagnosis between oncocytoma and chromophobe RCC. Furthermore, we found that ARPP was selectively expressed in part of the distal renal tubule in normal kidney. Immunoelectron microscopy with anti-ARPP antibody revealed that ARPP was localized in mitochondria and nuclei in both the normal distal renal tubule and oncocytoma, suggesting that oncocytoma may be derived from the distal nephron, and probably from part of the distal renal tubule.

Molecular classification of renal tumors by gene expression profiling

Renal tumor classification is important because histopathological subtypes are associated with distinct clinical behavior. However, diagnosis is difficult because tumor subtypes have overlapping microscopic characteristics. Therefore, ancillary methods are needed to optimize classification. We used oligonucleotide microarrays to analyze 31 adult renal tumors, including clear cell renal cell carcinoma (RCC), papillary RCC, chromophobe RCC, oncocytoma, and angiomyolipoma. Expression profiles correlated with histopathology; unsupervised algorithms clustered 30 of 31 tumors according to appropriate diagnostic subtypes while supervised analyses identified significant, subtype-specific expression markers. Clear cell RCC overexpressed proximal nephron, angiogenic, and immune response genes, chromophobe RCC oncocytoma overexpressed distal nephron and oxidative phosphorylation genes, papillary RCC overexpressed serine protease inhibitors, and extracellular matrix products, and angiomyolipoma overexpressed muscle developmental, lipid biosynthetic, melanocytic, and distinct angiogenic factors. Quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry of formalin-fixed renal tumors confirmed overexpression of proximal nephron markers (megalin/low-density lipoprotein-related protein 2, alpha-methylacyl CoA racemase) in clear cell and papillary RCC and distal nephron markers (beta-defensin 1, claudin 7) in chromophobe RCC/oncocytoma. In summary, renal tumor subtypes were classified by distinct gene expression profiles, illustrating tumor pathobiology and translating into novel molecular bioassays using fixed tissue.

KIT expression in chromophobe renal cell carcinoma: comparative immunohistochemical analysis of KIT expression in different renal cell neoplasms

The overexpression of c-Kit in chromophobe renal cell carcinoma (ChRCC) has been described by comparative gene expression analyses and has been proposed as a possible specific hallmark of this neoplasm. The aim of our study was to establish its immunohistochemical expression in a large series of ChRCC and to compare it with other renal neoplasms. In our study, immunohistochemical characterization of KIT was performed in 87 renal neoplasms including 25 cases of ChRCC, 13 cases of renal oncocytoma, and 39 renal cell carcinomas (21 cases of conventional RCC [CRCC], 8 cases of CRCC with granular cell differentiation, and 10 cases of papillary RCC [PRCC]). Eighty-eight percent ChRCC and 71% oncocytomas showed immunohistochemical expression of KIT, while the other types of RCC studied were all negative. The meaning of immunohistochemical expression of KIT in ChRCC and oncocytomas is still unknown, but its immunohistochemical staining appears to be useful in distinguishing ChRCC from PRCC, CRCC, and its granular cell variant. Moreover, our findings support current models that consider that there is a histopathogenic relationship between oncocytoma and ChRCC. Finally, it should be determined whether KIT plays a role in the tumorigenesis of ChRCC and oncocytoma and whether targeted therapy with STI-571, an inhibitor of KIT, could be effective in exceptional cases of ChRCC with metastatic extension or recurrence.

Beta defensin-1, parvalbumin, and vimentin: a panel of diagnostic immunohistochemical markers for renal tumors derived from gene expression profiling studies using cDNA microarrays

The common histopathologic subtypes of renal epithelial neoplasms include conventional, or clear cell, renal cell carcinoma (RCC), papillary RCC, chromophobe RCC, and renal oncocytoma. These subtypes differ clinically and pathologically, making accurate classification important. However, this differential diagnosis can be challenging because of overlapping morphology, suggesting a potential utility for ancillary immunohistochemical markers. We used cDNA microarrays to identify candidate markers for distinguishing renal tumor subtypes. In this report we validated differential expression of three candidate markers, beta defensin-1, parvalbumin, and vimentin, and evaluated the use of this immunohistochemical panel as a potential diagnostic tool. Consistent with our cDNA microarray data, chromophobe RCCs and oncocytomas exhibited similar expression profiles: 8 of 8 examples of each subtype were immunohistochemically positive for beta defensin-1 and parvalbumin and negative for vimentin (sensitivity 100%, specificity 100%); 4 of 7 papillary RCCs were positive for beta defensin-1, parvalbumin, and vimentin (sensitivity 57%, specificity 97%); and 22 of 23 conventional RCCs were negative for beta defensin-1, parvalbumin, or both markers (sensitivity 96%, specificity 96%) as well as positive for vimentin (sensitivity 83%). The immunohistochemical panel distinguished renal tumor subtypes with greater specificity than any marker used alone. This work demonstrates that a useful panel of immunohistochemical markers can be derived from differential gene expression profiles determined using cDNA microarrays.

Expression profiling of renal epithelial neoplasms: a method for tumor classification and discovery of diagnostic molecular markers

The expression patterns of 7075 genes were analyzed in four conventional (clear cell) renal cell carcinomas (RCC), one chromophobe RCC, and two oncocytomas using cDNA microarrays. Expression profiles were compared among tumors using various clustering algorithms, thereby separating the tumors into two categories consistent with corresponding histopathological diagnoses. Specifically, conventional RCCs were distinguished from chromophobe RCC/oncocytomas based on large-scale gene expression patterns. Chromophobe RCC/oncocytomas displayed similar expression profiles, including genes involved with oxidative phosphorylation and genes expressed normally by distal nephron, consistent with the mitochondrion-rich morphology of these tumors and the theory that both lesions are related histogenetically to distal nephron epithelium. Conventional RCCs underexpressed mitochondrial and distal nephron genes, and were further distinguished from chromophobe RCC/oncocytomas by overexpression of vimentin and class II major histocompatibility complex-related molecules. Novel, tumor-specific expression of four genes-vimentin, class II major histocompatibility complex-associated invariant chain (CD74), parvalbumin, and galectin-3-was confirmed in an independent tumor series by immunohistochemistry. Vimentin was a sensitive, specific marker for conventional RCCs, and parvalbumin was detected primarily in chromophobe RCC/oncocytomas. In conclusion, histopathological subtypes of renal epithelial neoplasia were characterized by distinct patterns of gene expression. Expression patterns were useful for identifying novel molecular markers with potential diagnostic utility.

Histogenetic stereological reconstruction of rat basophilic, clear, and oncocytic neoplastic renal cell lesions using carbonic anhydrase type II-PAS double-stained sections

The histogenesis of 3 types of rat renal cell tumors (basophilic cell, clear cell, and oncocytic) was stereologically analyzed, with particular attention paid to transitions from normal tubules. Early nitrosamine-induced preneoplastic lesions, including dysplastic tubules (altered tubules), epithelial hyperplasias, and small adenomas, were reconstructed using serially sectioned specimens processed for carbonic anhydrase type II (CA) and periodic acid-Schiff (PAS) (CA-PAS) double staining to allow easier distinction of the nephron segments: Proximal tubules had a PAS-positive brush border and were weakly positive for CA in the cytoplasm; distal tubules were PAS negative and weakly positive for CA; collecting ducts were PAS negative and strongly positive for CA. Similarly, cytochrome c oxidase (CytOx) and CytOx-PAS double staining was also applied to confirm the character of oncocytic lesions. All basophilic lesions (7 of 7) showed transition to proximal tubules. Clear cell lesions positive for CA, on the other hand, showed transition to distal tubules in 4 of 9 (44.4%) lesions and to collecting ducts in 4 of 9 (44.4%) lesions, but in only 1 of 9 (11%) to a proximal tubule. All oncocytic lesions (16 of 16), characterized by positivity for both CA and CytOx, showed transition to collecting ducts. The results indicate that the origins of renal cell neoplasia are proximal tubules for the basophilic cell lesions, either proximal or distal tubules for their clear cell counterparts, and collecting ducts for oncocytic lesions.

Retrospective evaluation of c-erbB-2 oncogene amplification using competitive PCR in collecting duct carcinoma of the kidney

PURPOSE

To evaluate retrospectively c-erbB-2 oncogene amplification in paraffin embedded specimens of collecting duct carcinoma of the kidney (CDC) with competitive polymerase chain reaction (PCR).

MATERIALS AND METHODS

Eleven CDC specimens were evaluated with a novel PCR procedure for oncogene amplification measurement, which provides sensitive and accurate results even in presence of low-quality DNA, unsuitable for Southern blot techniques.

RESULTS

c-erbB-2 oncogene amplification was present in 5 out of 11 cases (45%) with a number of copies ranging from 4 to 12. All patients presenting oncogene amplification decreased within one year, while 50% (3/6) of those without amplification are alive with a mean follow-up of 42 months.

CONCLUSIONS

The high incidence of c-erbB-2 oncogene amplification in CDC further characterizes this tumor as a separate entity from renal cell carcinoma, and shows some genetic characteristics in common with transitional cell carcinoma.

Renal tubular dysgenesis present in a newborn with meconium ileus

The combination of renal tubular dysgenesis (RTD) and meconium ileus in a native Israeli is presented for the first time. The clinical diagnosis was oligohydramnios and abruptio placentae, respiratory failure, and anuria refractory to treatment. The autopsy revealed meconium ileus and meconium peritonitis. RTD was established by the detection of a monomorphous undifferentiated population of tubules, absence of proximal tubules, and dense epithelial membrane antigen immunoreactivity of all tubules. The lack of alpha 1-antitrypsin- and lysozyme-immunoreactive tubules was first revealed in the kidney with RTD. These findings extend the possibilities of RTD detection.

Experimental models of kidney tumors

We here present in outline some outstanding results on the animal models of renal tumors submitted to the highest attention, which include two kinds of epithelial neoplasms: those developed from the epithelium lining each the renal tubules (renal cell tumors) and pelvis; the mesenchymal tumor of rat; and tumors with embryonal appearance: the nephroblastoma as well as the variant of it known as the estrogen-induced tumor in the hamster. The review deals with methods for tumor induction and the pathobiology of tumors, the latter mainly focused on the identification of the precise types of renal cells committed in tumor origin. The existence of closely related counterparts of these animal tumors in man is also emphasized, by representing a situation of great potentiality, already exploited, to improve understanding of both the nature and development of renal tumors in man.

Sialylated glycoconjugates in chromophobe cell renal carcinoma compared with other renal cell tumors. Indication of its development from the collecting duct epithelium

The present study was designed to shed light on the extraordinary histochemical properties of the chromophobe cell renal carcinoma detected by Hale's colloidal iron reaction. Special emphasis was laid on the lectin histochemical analysis of cytoplasmic glycoconjugates. Binding of peanut agglutinin (PNA) and Erythrina cristagalli agglutinin (ECA) after enzymatic release of sialic acid and direct binding of Dolichos biflorus agglutinin (DBA) correlates well with the expression of binding sites for Sambucus nigra agglutinin (SNA) and Maackia amurensis agglutinin (MAA) revealing abundant sialylated carbohydrate moieties within the cytoplasm. This characteristic binding pattern differs considerably from the faint staining observed in the majority of other renal carcinomas, thus confirming that the chromophobe cell renal carcinoma is a distinct entity. However, the lectin binding pattern of renal oncocytoma obviously resembles that of chromophobe carcinoma indicating a close relationship between these renal tumors. Detailed analysis of adjacent renal parenchyma revealed a lectin binding pattern quite similar to that described in the chromophobe carcinomas exclusively in the intercalated cells lining the collecting duct. This finding suggests that the chromophobe cell renal carcinoma originates from the collecting duct epithelium. The detection of small complexes consisting of altered epithelia which display the morphological characteristics of chromophobe carcinoma and the histochemical properties of intercalated cells probably indicates the emergence of preneoplastic lesions preceding the development of chromophobe carcinoma. Even though further studies are clearly needed to elucidate the physiological role of the cellular glycoconjugates detected, the present results already provide valuable insight into the histogenesis and pathogenesis of the chromophobe cell renal carcinoma.

Distribution of cytokeratins, vimentin and desmoplakins in normal renal tissue, renal cell carcinomas and oncocytoma as revealed by immunofluorescence microscopy

Forty-two renal cell carcinomas, one oncocytoma and normal renal tissue were studied for the presence of cytokeratins and vimentin. The investigations were performed by immunofluorescence microscopy applying a panel of mono- and polyclonal antibodies to intermediate filament proteins. In all tumours except chromophobic renal cell carcinoma (CRCC) and oncocytoma a co-expression of cytokeratins and vimentin could be shown. The intermediate filament expression was often, however, very heterogeneous particularly with respect to the distribution of cytokeratins and vimentin, to the clonality of the antibodies used and to the tumour areas studied. The latter could be impressively demonstrated by examining a whole tumour. In CRCC and oncocytoma all tumour cells expressed cytokeratins and, in addition, single tumour cells also expressed vimentin. In normal renal tissue we could show vimentin-positive epithelia of proximal and distal tubules, which is reported for the first time.

Oncocytic adrenal cortical carcinoma

A case of adrenal cortical carcinoma composed of mitochondria-rich cells is reported. The cells contained condensed zones and loose whorls of smooth endoplasmic reticulum. Crystalline matrical inclusions were present in some of the mitochondria, whereas others contained round, homogeneous, dense matrical inclusions. Flow cytometry revealed a hyperdiploid stem line with a DNA index of 1.3.

Case report: characteristic ultrasonographic appearance of a large renal oncocytoma

The sonographic appearance of a large renal oncocytoma is described. The 'spoke-wheel' of hypoechoic radiating bands within the tumour was found to correlate closely with other imaging modalities and the histopathological appearance of the surgical specimen. This characteristic sonographic picture, which appears to be a feature of size, enabled a confident pre-operative diagnosis to be made.

Immunohistochemical identification of tubular segments in percutaneous renal biopsies

To identify the renal cortical tubular segments involved in tubulo-interstitial disease in formalin-fixed, paraffin-embedded percutaneous kidney biopsies, we developed multiple immunolabeling protocols using segment-specific tubular markers. The present study of biopsies from patients with minimal change or thin basement membrane nephropathy provides a baseline for interpretation of histopathology. Proximal tubules were stained either by the PAS reaction or by the biotinylated Phaseolus vulgaris erythroagglutinin (PHA-E)-streptavidin-gold-silver system (brush borders black). The anti-Tamm-Horsfall (THP) antibody-immunoperoxidase (aminoethylcarbazole, AEC-IPO), and anti-epidermal cytokeratins (ECK) antibodies-immunoalkaline-Fast Blue BB methods marked the distal straight tubules and the cortical collecting system red-brown and blue, respectively. When these immunolabelings were combined, the coapplication of AEC-PO-labeled peanut agglutinin (PNA) or anti-epithelial membrane antigen antibody-AEC-IPO technique (both are markers for distal nephron) visualized the apical membranes of distal convoluted tubules. In the protocol PHA-E + PNA + THP + ECK, the tubular basement membranes were outlined by the anti-laminin antibody-AEC-IPO staining, carried out simultaneously. The protocol PNA + THP + ECK + PAS was found to be quite appropriate multiple immunolabeling method for the tubules, and is recommended for use as a tool in the study of tubulo-interstitial diseases.

Bellini duct carcinoma: further evidence for this rare variant of renal cell carcinoma

Bellini duct carcinomas have recently been identified as a new entity in the spectrum of renal cell carcinomas and 10 cases have now been reported. The present paper adds detailed clinical and morphological data on six new cases. In addition, immunohistological and electronmicroscopical results support the origin of these tumours from the renal collecting ducts, especially the papillary ducts (Bellini ducts). A set of immunohistological reactions, including reactions to cytokeratins 13 and 19, vimentin and UEA-1 was found to facilitate the differential diagnosis of Bellini duct carcinomas from other renal cell carcinomas and infiltrating urothelial carcinomas of renal pelvis.

Differential diagnosis of histogenetically distinct human epithelial renal tumours with a monoclonal antibody against gamma-glutamyltransferase

The localization of membrane-bound gamma-glutamyltransferase with monoclonal antibody (mAb) 138H11 proved to be of value for differential diagnosis of renal cancer, since it correlated with the histogenetic profile of human epithelial renal tumors. Immunoreactive gamma-glutamyltransferase was located in the proximal tubule in all normal human kidneys (15/15) examined thus far by both ultrastructural and immunohistochemical techniques. From 68 epithelial renal cancers tested 31/31 clear-cell carcinomas and 15/16 chromophilic carcinomas expressed the target epitope of mAb 138H11. In contrast, 0/11 oncytomas, 0/9 chromophobic carcinomas, and 0/1 Duct-Bellini carcinoma were immunoreactive. These results support a model of histogenesis and classification of epithelial renal tumours, according to which clear-cell and chromophilic renal carcinomas originate from transformed proximal tubule cells, whereas oncocytomas, chromophilic and Duct-Bellini carcinomas originate from cells of the collecting duct.

[Classification of renal cell carcinoma/tumors and their relationship to the nephron-collecting tubules system]

After a controversial phase of nomenclature (including--among others--the terms "hypernephroma" and "hypernephroid carcinoma") a cytomorphologically defined subtyping of renal cell tumours (adenomas, carcinomas, oncocytomas) is offered, based on new electron microscopical and histochemical observations. These data are in part supported by cytogenetical findings reported in the literature. Phenotypical/histogenetical relations to different parts or cell types, respectively, of the nephron-collecting duct system could be demonstrated. Chromophobe cell carcinoma and oncocytoma exhibit features of the intercalated cells.

Collecting duct origin of rat renal clear cell tumors

The renal tubular segment from which clear cell tumors originate was investigated in the kidneys of rats treated with N-nitrosomorpholine. This tumor type, which in the rat closely resembles that in man, is made up of clear and granular acidophilic cells and arises from tubules lined by clear cells. The tubular origin of the tumors was established in serial sections by demonstrating connections between both clear cell tumors and tubules lined by clear cells, and renal tubules of normal appearance. In 45 clear cell lesions (17 tumors and 28 tubules) one or more such connections were identified which belonged to the collecting system. In accordance with their localisation in the kidney, the clear cell lesions were connected predominantly to tubules of the cortical collecting system and occasionally to outer medullary collecting ducts. As previously reported, oncocytic tubules and microoncocytomas were observed to originate from the same portions of the collecting system. Rarely, microadenomas and tubules consisting of both oncocytes and clear or granular acidophilic cells were also observed in the kidneys studied.

The human chromophobe cell renal carcinoma: its probable relation to intercalated cells of the collecting duct

In the present study we have examined ten cases of the chromophobe type renal cell carcinoma. This type of tumor is distinguished from the other carcinomas of the kidney with light cytoplasm (formerly called "hypernephroid") by (a) a positive Hale's iron colloid stain of the cytoplasm, (b) the occurrence of numerous invaginated vesicles within the cytoplasm that resemble the invaginated vesicles of intercalated cells of the collecting duct system, and (c) a positive immunoreaction of both the plasma membrane and the cytoplasm with antibodies to the epithelial membrane antigen (EMA) and carbonic anhydrase C (CAC), respectively. Unlike oncocytomas, which also express CAC and EMA, the chromophobe renal cell carcinoma does not express the erythrocyte anion exchanger band 3. These findings strongly indicate that chromophobe renal cell carcinomas as well as oncocytomas of the kidney are histogenetically related to the two populations of intercalated cells of the collecting duct system. Thus, both tumors represent examples of renal tumors which disprove the broadly accepted hypothesis that all epithelial tumors of the kidney are histogenetically related to the proximal tubule.