Ultrastructural spectrum of oncocytic and chromophobe renal tumors: Insights from osmium maceration-based scanning electron microscopy of formalin-fixed tissues.

BackgroundChRCC is a rare form of kidney cancer and presents with a poor prognosis in the metastatic setting, with limited response to immune checkpoint inhibitors (ICI) and targeted therapy. While previous studies suggested that ChRCC originates from intercalated cells of the kidney, its exact cellular origin has not been clearly defined. We therefore investigated the cellular origin of ChRCC and renal oncocytic neoplasms at single-cell resolution.MethodsChRCC, renal oncocytoma (RO) and low-grade oncocytic tumor (LOT) samples with matched normal kidney specimens were analyzed using single-cell RNA sequencing (scRNA-seq). Epithelial cells from normal samples were clustered and annotated into the distinct known cellular types found in the adult healthy human kidney. A logistic regression model (Young M.D. et al., Science, 2018) was trained on the normal epithelial clusters, using a comprehensive set of 74 marker genes (features). Subsequently, the model was tested on tumor clusters from ChRCC, RO and LOT to investigate their cellular origin through the identification of the highest predicted probabilities of similarity between normal epithelial cellular types and tumor cells. Differential gene expression and pathway analyses between ChRCC and its cell of origin were then conducted to investigate mechanisms of oncogenesis.ResultsFollowing quality-control, 46,817 cells from 5 tumors (ChRCC: n=3, RO: n=1 and LOT: n=1) and 4 normal samples were isolated for scRNA-seq analysis. Among normal samples, 784 epithelial cells were clustered and annotated into the following cellular entities: proximal tubule (PT), loop of Henle – distal tubule (LOH-DT), principal cells (PC), α-intercalated cells (ICA) and β-intercalated cells (ICB). Across all ChRCC and oncocytic tumors, 7,573 tumor cells were identified, among which 7,425 corresponded to ChRCC. For ChRCC, RO, and LOT neoplasms, the highest predicted probability of similarity was consistently identified with ICA cells (ranging from 0.60 to 0.80). This finding was validated using an external and previously published (Zhang Y. et al., Proc Natl Acad Sci USA, 2021) scRNA-seq dataset from a patient with ChRCC (n=2,853 cells). Additionally, evaluation of previously defined ChRCC-specific markers (i.e. FOXI1, RHCG, KIT, CLCNKA, and CLCNKB) in scRNA-seq data of normal kidney epithelial cells consistently showed the highest expression in ICA cells. Differential gene expression between ChRCC and ICA cells revealed a significant downregulation of MHC class I genes (i.e. HLA-A , HLA-B, and HLA-C) and HSP70 (family A) genes (i.e. HSPA1A, HSPA1B, HSPA6, and HSPA8) in ChRCC. Differential pathway analysis between ChRCC and ICA cells showed a significant enrichment of the ferroptosis, glutathione metabolism, mTOR signaling and IL-15 pathways in ChRCC.ConclusionsRenal oncocytic tumors, including ChRCC, appear to originate from the α-intercalated cells of the normal human kidney. As compared to α-intercalated cells, ChRCC downregulates MHC class I genes, which may be associated with its poor response to immunotherapy. Further, the selective downregulation of HSP70 genes may in part explain ChRCC’s increased sensitivity to ferroptosis.CDMRP DOD Funding: yes

The goal of this study was to evaluate the morphology, immunoprofile, and management of renal oncocytoma (RO), hybrid oncocytic tumor (HOT), and chromophobe renal cell carcinoma (ChRCC). Forty-seven cases of RO, 7 cases of HOT, and 25 cases of ChRCC were included in the study. Tissue microarrays were prepared for immunohistochemical evaluation. Large sheets of cells with transverse vessels, and higher nuclear grade were seen more often in ChRCC than in RO or HOT. Tumor cells of RO were more uniform in size and shape relative to HOT and ChRCC. The cytoplasmic features of RO were more uniformly granular relative to HOT and ChRCC, which exhibited variable cytoplasmic features. CK7 and MUC1 were expressed more frequently and diffusely in ChRCC (54% and 94%, respectively) than RO (4% and 52%, respectively) and HOT (0% and 71%, respectively). AMACR and PAX8 were more frequently expressed diffusely in RO (67% and 42%, respectively) than in HOT (0% and 0%, respectively) or ChRCC (14% and 11%, respectively). Most HOT (57%) and CHRCC (60%) patients underwent nephrectomy. Cryoablation was the treatment of choice for 24% of patients with ChRCC, 2% of patients with RO, and 0% of patients with HOT. The majority of patients with RO (88%) opted for active surveillance-a much higher rate than that for patients with HOT (29%) or ChRCC (12%). Some cytologic features and immunomarkers are useful in differentiating RO, HOT, and ChRCC. Because no immunomarker or morphologic finding is specific by itself, a combination of morphologic features with immunohistochemistry appears to be the most reliable way to distinguish ChRCC, HOT, and RO on biopsy samples. Subclassification of renal oncocytic tumors into specific categories impacts clinical management and downstream treatment selection.

"Other oncocytic renal tumors of the kidney" is a new category constituted by 2022 WHO classification and different in the point of morphology and immunohistochemistory from typical oncocytic/eosinophilic renal tumors including chromophobe renal cell carcinoma and oncocytoma. The patient was an 84-year-old woman in whom a left renal tumor was incidentally discovered. She underwent left nephrectomy, and the pathological specimens showed a borderline eosinophilic renal tumor between chromophobe renal cell carcinoma and renal oncocytoma. After all recognized oncocytic tumors were excluded, we diagnosed the tumor as other oncocytic renal tumor of the kidney. Other oncocytic renal tumor of the kidney is a provisional category. Therefore, further research and accumulation of similar cases are necessary.

4549 Background: ChRCC represents about 5% of all kidney cancer and has a dismal prognosis in the metastatic setting, with limited response to immune checkpoint inhibitors (ICI) and targeted therapy. We evaluated the molecular properties of ChRCC and related oncocytic neoplasms to define the tumor immune microenvironment and identify potential therapeutic strategies. Methods: ChRCC, renal oncocytoma (RO) and low-grade oncocytic tumor (LOT) samples with matched normal kidney specimens were evaluated using single-cell RNA sequencing (scRNA-seq) and single-cell T-cell receptor sequencing (scTCR-seq). T-cell antigenic specificities from scTCR-seq were inferred using a comprehensive database of annotated T-cell receptor sequences (VDJdb). The infiltration of CD45+ immune cells in renal oncocytic tumors and ccRCC samples was quantified using immunohistochemistry (IHC). Bulk RNA-sequencing (RNA-seq) data of clear cell RCC (ccRCC) and ChRCC were further analyzed using The Cancer Genome Atlas (TCGA) KIRC and KICH cohorts, respectively, with immune cell fractions calculated using CIBERSORTx. Results: After quality-control, 46,817 cells from 5 tumor (ChRCC: n = 3, RO: n = 1 and LOT: n = 1) and 4 normal samples were isolated for scRNA-seq analysis. Renal oncocytic tumors (ChRCC, RO, and LOT) had a low density of CD45+ cells (mean: 739 ± 114 cells/mm2; n = 5) compared to ccRCC (mean: 3,420 ± 1,979 cells/mm2; n = 5) (p < 0.05). Across all tumors, CD8+ T-cell clusters displayed a low expression of immune exhaustion markers (i.e. PDCD1 [PD-1], CTLA4, LAG3, HAVCR2 [TIM-3], and TIGIT). Analysis of TCGA bulk RNA-seq data after adjustment for CD8 T-cell fraction showed no difference in the expression of most immune exhaustion markers (i.e. PDCD1, CTLA4, LAG3) in ChRCC compared to normal samples (p > 0.05), contrasting with a substantially higher expression in ccRCC versus normal kidney (p < 0.05). Analysis of the T-cell repertoire (scTCR-seq) of ChRCC, RO and LOT samples did not identify a pattern of clonal expansion, and a considerable proportion of clonotypes were inferred to have specificity for viral antigens (range: 1.3 to 34.4% among all samples; 11.3 to 34.4% after filtering out two samples with a low ( < 300) number of T-cells). Conclusions: Renal oncocytic tumors, including ChRCC, exhibit a low infiltration of immune cells, a non-exhausted immune phenotype and, a lack of clonally expanded tumor-specific T-cells. These findings may partially explain the molecular basis for the lack of response to ICIs in advanced ChRCC and outline the unique exhaustion phenotype of renal oncocytic tumors.

4558 Background: ChRCC is an uncommon kidney cancer variant that has a poor prognosis in the metastatic setting, with limited response to current standard-of-care immune checkpoint inhibitors (ICIs) used for other RCC histologies. We evaluated the tumor-immune microenvironment of ChRCC and other related oncocytic neoplasms to better understand the immunophenotype of these tumors. Methods: We performed paired single-cell RNA sequencing (scRNA-seq), single-cell T-cell receptor sequencing (scTCR-seq), and CD45 immunohistochemistry (IHC) of ChRCC, renal oncocytoma (RO) and low-grade oncocytic tumor (LOT) tumor and matched normal samples. Bulk RNA-sequencing (RNA-seq) data of clear cell RCC (ccRCC), papillary RCC (pRCC) and ChRCC were additionally analyzed using The Cancer Genome Atlas (TCGA) kidney cancer cohorts. T cell antigenic specificities from scTCR-seq were inferred using a comprehensive database of annotated T-cell receptor sequences (VDJdb). Single-cell transcriptomic signatures were used to infer the tumor specificity (Oliveira G, Nature, 2021 and Lowery FJ, Science, 2022) and viral specificity (Oliveira G, Nature, 2021) of CD8+ T-cells from ChRCC, as compared to those from ccRCC (Braun DA, Cancer Cell, 2021). Results: ChRCC and other oncocytic tumors had a lower infiltration of CD45+ immune cells as compared to ccRCC (p<0.01). Single-cell analysis was performed on 46,817 cells from 5 tumors (ChRCC: n=3, RO: n=1 and LOT: n=1) and 4 normal samples. Across all tumors, CD8+ T cell clusters displayed a lower expression of immune checkpoints (i.e. PDCD1 [PD-1], CTLA4, LAG3, HAVCR2 [TIM-3], and TIGIT) as compared to ccRCC. This was further validated in a bulk RNA-seq analysis using TCGA data, with a significantly lower expression of all immune checkpoints in ChRCC compared to both ccRCC (p<0.01) and papillary RCC (pRCC; p<0.01). Analysis of the T cell receptor repertoire (scTCR-seq) of ChRCC, RO and LOT samples did not show any pattern of clonal expansion, and a higher proportion of T cells in ChRCC were inferred to have a viral specificity, as compared to ccRCC (0.79 vs. 0.1%, respectively). CD8+ T cells from ChRCC (vs. ccRCC) displayed a significantly lower expression of two signatures of tumor specificity (p<0.01), and a higher expression of the viral-specific signature (p<0.01). Conclusions: In ChRCC, there is low infiltration by CD45+ immune cells. Although infiltrating CD8+ T cells have a predominantly non-exhausted immune phenotype, they likely lack anti-tumor specificity (i.e. are “bystander” T cells). These findings may help to understand the molecular basis for the lack of response to immunotherapy recently identified among patients with advanced ChRCC, and support future therapeutic strategies to increase infiltration of tumor-specific T cells into the tumor microenvironment.

Claudin-7 and claudin-8: immunohistochemical markers for the differential diagnosis of chromophobe renal cell carcinoma and renal oncocytoma

<div>Abstract<p><b>Purpose:</b> The diagnostic differential for CD117/KIT(+) oncocytic renal tumor biopsies is limited to benign renal oncocytoma versus chromophobe renal cell carcinoma (ChRCC); however, further differentiation is often challenging and requires surgical resection. We investigated clinical variables that might improve preoperative differentiation of CD117(+) renal oncocytoma versus ChRCC to avoid the need for benign tumor resection.</p><p><b>Experimental Design:</b> A total of 124 nephrectomy patients from a single institute with 133 renal oncocytoma or ChRCC tumors were studied. Patients from 2003 to 2012 comprised a retrospective cohort to identify clinical/radiographic variables associated with renal oncocytoma versus ChRCC. Prospective validation was performed among consecutive renal oncocytoma/ChRCC tumors resected from 2013 to 2017.</p><p><b>Results:</b> Tumor size and younger age were associated with ChRCC, and multifocality with renal oncocytoma; however, the most reliable variable for ChRCC versus renal oncocytoma differentiation was the tumor:cortex peak early-phase enhancement ratio (PEER) using multiphase CT. Among 54 PEER-evaluable tumors in the retrospective cohort [19 CD117(+), 13 CD117(−), 22 CD117-untested], PEER classified each correctly as renal oncocytoma (PEER >0.50) or ChRCC (PEER ≤0.50), except for four misclassified CD117(−) ChRCC variants. Prospective study of PEER confirmed 100% accuracy of renal oncocytoma/ChRCC classification among 22/22 additional CD117(+) tumors. Prospective interobserver reproducibility was excellent for PEER scoring (intraclass correlation coefficient, ICC = 0.97) and perfect for renal oncocytoma/ChRCC assignment (ICC = 1.0).</p><p><b>Conclusions:</b> In the largest clinical comparison of renal oncocytoma versus ChRCC to our knowledge, we identified and prospectively validated a reproducible radiographic measure that differentiates CD117(+) renal oncocytoma from ChRCC with potentially 100% accuracy. PEER may allow reliable biopsy-based diagnosis of CD117(+) renal oncocytoma, avoiding the need for diagnostic nephrectomy. <i>Clin Cancer Res; 24(16); 3898–907. ©2018 AACR</i>.</p></div>

Purpose: The diagnostic differential for CD117/KIT(+) oncocytic renal tumor biopsies is limited to benign renal oncocytoma versus chromophobe renal cell carcinoma (ChRCC); however, further differentiation is often challenging and requires surgical resection. We investigated clinical variables that might improve preoperative differentiation of CD117(+) renal oncocytoma versus ChRCC to avoid the need for benign tumor resection.Experimental Design: A total of 124 nephrectomy patients from a single institute with 133 renal oncocytoma or ChRCC tumors were studied. Patients from 2003 to 2012 comprised a retrospective cohort to identify clinical/radiographic variables associated with renal oncocytoma versus ChRCC. Prospective validation was performed among consecutive renal oncocytoma/ChRCC tumors resected from 2013 to 2017.Results: Tumor size and younger age were associated with ChRCC, and multifocality with renal oncocytoma; however, the most reliable variable for ChRCC versus renal oncocytoma differentiation was the tumor:cortex peak early-phase enhancement ratio (PEER) using multiphase CT. Among 54 PEER-evaluable tumors in the retrospective cohort [19 CD117(+), 13 CD117(-), 22 CD117-untested], PEER classified each correctly as renal oncocytoma (PEER >0.50) or ChRCC (PEER ≤0.50), except for four misclassified CD117(-) ChRCC variants. Prospective study of PEER confirmed 100% accuracy of renal oncocytoma/ChRCC classification among 22/22 additional CD117(+) tumors. Prospective interobserver reproducibility was excellent for PEER scoring (intraclass correlation coefficient, ICC = 0.97) and perfect for renal oncocytoma/ChRCC assignment (ICC = 1.0).Conclusions: In the largest clinical comparison of renal oncocytoma versus ChRCC to our knowledge, we identified and prospectively validated a reproducible radiographic measure that differentiates CD117(+) renal oncocytoma from ChRCC with potentially 100% accuracy. PEER may allow reliable biopsy-based diagnosis of CD117(+) renal oncocytoma, avoiding the need for diagnostic nephrectomy. Clin Cancer Res; 24(16); 3898-907. ©2018 AACR.

<div>Abstract<p><b>Purpose:</b> The diagnostic differential for CD117/KIT(+) oncocytic renal tumor biopsies is limited to benign renal oncocytoma versus chromophobe renal cell carcinoma (ChRCC); however, further differentiation is often challenging and requires surgical resection. We investigated clinical variables that might improve preoperative differentiation of CD117(+) renal oncocytoma versus ChRCC to avoid the need for benign tumor resection.</p><p><b>Experimental Design:</b> A total of 124 nephrectomy patients from a single institute with 133 renal oncocytoma or ChRCC tumors were studied. Patients from 2003 to 2012 comprised a retrospective cohort to identify clinical/radiographic variables associated with renal oncocytoma versus ChRCC. Prospective validation was performed among consecutive renal oncocytoma/ChRCC tumors resected from 2013 to 2017.</p><p><b>Results:</b> Tumor size and younger age were associated with ChRCC, and multifocality with renal oncocytoma; however, the most reliable variable for ChRCC versus renal oncocytoma differentiation was the tumor:cortex peak early-phase enhancement ratio (PEER) using multiphase CT. Among 54 PEER-evaluable tumors in the retrospective cohort [19 CD117(+), 13 CD117(−), 22 CD117-untested], PEER classified each correctly as renal oncocytoma (PEER >0.50) or ChRCC (PEER ≤0.50), except for four misclassified CD117(−) ChRCC variants. Prospective study of PEER confirmed 100% accuracy of renal oncocytoma/ChRCC classification among 22/22 additional CD117(+) tumors. Prospective interobserver reproducibility was excellent for PEER scoring (intraclass correlation coefficient, ICC = 0.97) and perfect for renal oncocytoma/ChRCC assignment (ICC = 1.0).</p><p><b>Conclusions:</b> In the largest clinical comparison of renal oncocytoma versus ChRCC to our knowledge, we identified and prospectively validated a reproducible radiographic measure that differentiates CD117(+) renal oncocytoma from ChRCC with potentially 100% accuracy. PEER may allow reliable biopsy-based diagnosis of CD117(+) renal oncocytoma, avoiding the need for diagnostic nephrectomy. <i>Clin Cancer Res; 24(16); 3898–907. ©2018 AACR</i>.</p></div>

Background: Chromophobe renal cell carcinoma (ChRCC) represents 5% of all kidney cancers. In contrast to clear cell RCC (ccRCC), the immune landscape of ChRCC and its response to immunotherapy remain poorly characterized. We sought to evaluate the clinical outcomes of patients with ChRCC treated with immuno-oncology (IO)-based regimens, and assess the immune cell composition, phenotypic state, and T cell specificity in the tumor microenvironment of ChRCC. Methods: Using real-world data from the International Metastatic RCC Database Consortium, we analyzed the survival outcomes and objective responses of patients with advanced ChRCC to currently adopted IO-based regimens (i.e. dual IO therapy or IO + vascular endothelial growth factor targeted therapy [VEGF-TT]) in the first-line setting, as compared to patients with ccRCC. Single-cell RNA sequencing (scRNA-seq) and single-cell T-cell receptor sequencing (scTCR-seq) were performed on ChRCC and related oncocytic neoplasms (i.e. renal oncocytoma [RO] and low-grade oncocytic tumor [LOT]) samples with matched normal kidney specimens. The infiltration of CD45+ immune cells in renal oncocytic tumors and ccRCC samples was quantified using immunohistochemistry (IHC). Results: Compared to patients with ccRCC (n=856) treated with first-line IO-based regimens, patients with ChRCC (n=31) had a lower overall survival (median: 24.7 vs. 50.5 months, p<0.001) and lower time to treatment failure (median: 4.5 vs. 11.0 months, p<0.001). Similarly, patients with ChRCC had a significantly lower overall response rate than those with ccRCC (12.0 vs. 47.1%, respectively; p<0.001). When evaluating immune cell infiltration, renal oncocytic tumors (ChRCC, RO, and LOT) exhibited a low density of CD45+ cells (mean: 739 ± 114 cells/mm2; n=5) compared to ccRCC (mean: 3,420 ± 1,979 cells/mm2; n=5) (p<0.05). Single-cell analysis was performed on 46,817 cells from 5 tumors (ChRCC: n=3, RO: n=1 and LOT: n=1) and 4 samples from adjacent normal kidney. Across all tumors, CD8+ T cell clusters displayed a lower expression of immune checkpoints (i.e. PDCD1, CTLA4, LAG3, HAVCR2, and TIGIT) as compared to CD8+ T-cells from ccRCC. This was further validated in the analysis of bulk RNA-seq data from the TCGA, with a significantly lower expression of all immune checkpoints in ChRCC compared to both ccRCC (p<0.01) and papillary RCC (pRCC; p<0.01). Analysis of the T cell receptor repertoire (scTCR-seq) of ChRCC, RO and LOT samples did not show any pattern of clonal expansion, and a higher proportion of T cells in ChRCC were inferred to have a viral specificity, compared to ccRCC (0.79 vs. 0.1%, respectively). Conclusions: Patients with metastatic ChRCC appear to display poor clinical outcomes when treated with IO-based regimens, compared to ccRCC. Renal oncocytic tumors, including ChRCC, exhibit a low infiltration of immune cells, and a non-exhausted immune phenotype. Citation Format: Michel Alchoueiry, Chris Labaki, Long Zhang, Yue Hou, Kevin Bi, Charbel Hobeika, J. Connor Wells, Kosuke Takemura, Ziad Bakouny, Sabrina Camp, Carmen Priolo, Damir Khabibullin, Nicholas Schindler, Renee Maria Saliby, Eddy Saad, Samer Salem, Melissa Daou, Rana McKay, Sumanta Pal, Daniel Heng, Eliezer Van Allen, Sachet Shukla, Toni Choueiri, David Braun, Elizabeth Henske. Clinical and molecular characterization of chromophobe renal cell carcinoma: A focus on immunotherapy based regimens and the tumor immune microenvironment [abstract]. In: Proceedings of the AACR Special Conference: Advances in Kidney Cancer Research; 2023 Jun 24-27; Austin, Texas. Philadelphia (PA): AACR; Cancer Res 2023;83(16 Suppl):Abstract nr B019.

Distinguishing renal oncocytoma (RO) from the eosinophilic variant of chromophobe renal cell carcinoma (ChRCC) under the light microscope is a common diagnostic problem. Our recent research has shown significant difference between the presence of tumor fibrous capsule in ChRCCs and ROs. Transforming growth factor beta 1 (TGF-β1) is a potent cytokine involved in regulating a number of cellular processes. Two main purposes of this research were to investigate whether the TGF-β1 staining could be related to the presence of tumor fibrous capsule and if it could be used in the differential diagnosis between ChRCC and RO. We investigated 34 cases: 16 ChRCCs (8 eosinophilic and 8 classic) and 18 ROs. All available slides of each tumor, routinely stained with hematoxylin and eosin (H&E) were first analyzed to note the presence of tumor fibrous capsule. One paraffin embedded tissue block matching the representative H&E slide was selected for the immunohistochemical analysis. TGF-β1 expression was analyzed semiquantitatively in the tumor tissue, the tumor fibrous capsule, if present and the peritumoral renal parenchyma. Intensity of TGF-β1 expression was weaker in ChRCCs than the one observed in ROs (P<0.05). The type of reaction in ChRCCs was predominantly membranous unlike in ROs, which exhibited a predominantly cytoplasmic reaction (P<0.05). Moreover, none of the ROs showed membranous type of reaction for TGF-β1. In the group of ChRCCs, tumors with capsule had statistically significant higher quantity of TGF-β1 expression in tumor tissue and in peritumoral renal parenchyma compared to the tumors without capsule (P<0.05). Our results showed different types of TGF-β1 expression in ChRCCs and ROs: ChRCCs had predominantly membranous type of reaction, and ROs predominantly cytoplasmic. Furthermore, ChRCCs with capsule had statistically significant higher quantity of TGF-β1 expression in tumor tissue and in peritumoral renal parenchyma compared to the tumors without capsule. Based on these findings we can speculate that it could be possible that TGF-β1 plays a role in the formation of fibrous capsule in ChRCCs.

Introduction. Renal neoplasms are a common disease. Differential diagnostics of different tumor subtypes for prognosis and treatment is necessary given that some of them, like renal cell oncocytomas, are benign, and others, like chromophobe renal cell carcinomas, are malignant. Unfortunately, the histological similarity between these tumors makes accurate diagnostics difficult. In some cases, additional diagnostic methods such as immunohistochemistry should be used. The aim of our study is to analyze the histological characteristics of chromophobe renal cell carcinomas and renal oncocytomas, in order to specify their pathognomonic features, allowing for the confirmation of the diagnosis. Materials and methods. We used data from histories of disease and histological postoperative material of 198 patients with chromophobe renal cell carcinoma and renal oncocytoma. After the diagnosis was confirmed, we described the histological features of the tumors and calculated their relative prevalence amongst the renal oncocytoma and chromophobe renal cell carcinoma tissues. To conclude, we identified the histological features that are more likely to be present in the case of chromophobe renal cell carcinoma. Conclusions. Chromophobe renal cell carcinomas are present in 31 % of our samples. Tumors are more prevalent in patients in their sixth and seventh decade. Most chromophobe renal cell carcinomas are unilateral. Chromophobe renal cell carcinomas have a polymorphic histological structure. The classic variant of chromophobe renal cell carcinoma is more common than the eosinophilic one. A mixed variant of chromophobe renal cell carcinoma is present in a minority of cases. The most common features of ChRCC are solid and alveolar growth patterns, clear and reticular cytoplasm, raisinoid nuclei. After comparing the relative prevalence of various histological features in renal oncocytomas to those present in chromophobe renal cell carcinomas, we are able to ascertain that chromophobe renal cell carcinomas tend to exhibit the following features significantly more often than renal oncocytomas: differing nuclear size, raisinoid nuclei, reticular cytoplasm, clear cytoplasm. The particular features mentioned in the preceding paragraph, can be present on a small subset of the tumor tissue, and are thus, often missed during analysis, which can lead to misdiagnosis. In order to mitigate this risk, we recommend analyzing a big sample of tumor tissue and using additive methods such as immunohistochemistry with biomarkers CD 10 (56C6), CD 68 (KP1), Cytokeratin 7 (OV-TL 12/30), CD117/c-kit, Vimentin (Vim3B4), S-100 (4C4.9).

The reliability of using fine-needle aspiration (FNA) to distinguish renal oncocytoma (RO), a benign tumor, from renal cell carcinoma (RCC), which has eosinophilic granular cytoplasm, has been questionable. However, it is clinically significant, because radical nephrectomy may be avoided in patients with RO. The authors retrospectively studied the cytologic features and ancillary study findings of RO compared with findings in RCCs with eosinophilic granular cytoplasm to evaluate the reliability of FNA-based diagnosis of RO. The authors reviewed 19 tumors, including 11 ROs, three chromophobe RCCs (CRCCs), three granular variant RCCs (GRCCs), and two eosinophilic variant papillary RCCs (EPRCCs). Smears and cell blocks were prepared using either computed tomography-guided or ultrasound-guided FNA material. Surgical specimens were available for all tumors. Cytokeratin, vimentin, and Hale colloidal iron (HCI) stains were performed on all 19 tumors. Electron microscopy (EM) was available for six tumors. Although most tumors demonstrated their classic cytologic features, the specific diagnosis using conventional smears or even core biopsies was difficult in some tumors, especially ROs, due to the overlapping cytomorphology among these tumors. Cytologic material was obtained from 10 of 11 RO specimens. Of 10 ROs, 8 original FNA-based diagnoses were oncocytic neoplasm. Immunoperoxidase studies revealed that all tumors of each type were positive for cytokeratin, whereas only GRCCs and EPRCCs were positive for vimentin. The two vimentin negative neoplasms, RO and CRCC, could be distinguished by HCI stain, which showed diffuse or focal cytoplasmic positivity in CRCCs and apical/perinuclear staining (73%) or negative staining (27%) in ROs. Ultrastructurally, cytoplasm densely packed with mitochondria was characteristic for oncocytoma. This study demonstrated that ROs can be distinguished reliably from RCCs on the basis of cytologic morphology combined with ancillary studies, including immunostaining with cytokeratin and vimentin antibodies and HCI stain. EM provides additional information to confirm the diagnoses.

Background: We review the pathological, cytopathological, and molecular features centered on renal oncocytoma and its differential diagnosis. The recent expansion of entities under the category of renal tumors with oncocytic or eosinophilic cytoplasm has important implications on how cytologic diagnosis is clinically considered. Summary: In this first of two parts, we discussed the pathological spectrum of oncocytic or eosinophilic tumors of the kidney that includes oncocytoma; chromophobe renal cell carcinoma (ChRCC) – including its eosinophilic variant (eosinophilic ChRCC); hybrid oncocytic/chromophobe tumors, either sporadic or syndromic; oncocytic papillary RCC, acquired cystic disease-associated RCC; succinate dehydrogenase (SDH)-deficient RCC; and eosinophilic solid and cystic (ESC) RCC. We describe the histomorphological and immunohistochemical features of these tumors, including the newly accepted entities, and focus on the molecular alterations reported. A practical approach for differential diagnosis and broader correlation to available cytologic findings are provided, with more in-depth cytologic descriptions for oncocytoma and eosinophilic ChRCC included in part 2 of this review. Most of the oncocytic tumors have an indolent behavior, although few aggressive cases have been reported in patients with ESC RCC, eosinophilic vacuolated tumor, and SDH-deficient RCC. Key Messages: In this era where surveillance management for low-grade oncocytic renal tumors is considered, precise diagnosis is important as it will have an impact on their subsequent management. Further, accurate diagnosis is important especially in renal tumors associated with hereditary neoplasms for monitoring and genetic counseling for their family members.

The distinction between chromophobe renal cell carcinoma, the granular cell variant of clear cell renal cell carcinoma, and renal oncocytoma is a common diagnostic dilemma. The usefulness of KIT, CD10, RCC, and RON in the differential diagnosis of these renal epithelial tumors was investigated. KIT was 100% positive in chromophobe renal cell carcinoma (11 of 11) and renal oncocytoma (12 of 12). The KIT staining pattern was identical in both tumor types, with cytoplasmic membrane attenuation, and fine granular cytoplasmic staining. In contrast, KIT was absent in all granular cell variants of clear cell renal cell carcinoma (0 of 6). RCC was observed in more than 80% of the granular cell variant of clear cell renal cell carcinoma (5 of 6) but was negative in all chromophobe renal cell carcinomas (0 of 11) and renal oncocytomas (0 of 12). CD10 was expressed in 100% of the granular cell variant of clear cell renal cell carcinoma (6 of 6), 72% of chromophobe renal cell carcinomas (8 of 11), and 58% of renal oncocytomas (7 of 12). RON was 100% positive in the chromophobe renal cell carcinomas (11 of 11) and renal oncocytomas (12 of 12) but only 50% positive in the granular cell variant of clear cell renal cell carcinoma (3 of 6). Colloidal iron was diffusely and strongly positive in more than 80% of the chromophobe renal cell carcinomas (9 of 11), focally and weakly positive in 41% of the renal oncocytomas (5 of 12) but negative in all granular cell variant of clear cell renal cell carcinoma (0 of 6). The above results demonstrate that: 1) KIT is a very sensitive marker for both chromophobe renal cell carcinoma and renal oncocytoma; 2) immunohistochemistry using antibodies to KIT combined with RCC was sufficient to discriminate between chromophobe renal cell carcinoma and the granular cell variant of clear cell renal cell carcinoma; and 3) neither RON, nor KIT, nor a combination of this panel can be used to distinguish chromophobe renal cell carcinoma from renal oncocytoma. Colloidal iron staining aided in this distinction for the majority of the chromophobe renal cell carcinomas (more than 80% positive) and renal oncocytomas (close to 60% negative).