Pelvic Cholelithiasis. A Report of 4 Cases

Introduction/Objective

Spillage of gallstones in the peritoneal cavity during laparoscopic cholecystectomy is a known intraoperative complication which could cause peritoneal irritation/abscess and occasionally present as ovarian cholelithiasis and pelvic mass. Our aim is to present the clinicopathologic findings of pelvic cholelithiasis in our institution.

Methods/Case Report

A one year computerized natural language search for “Halls, bile, pigment, crystals” in surgical final diagnosis and comment was performed. The patients’ demographic, clinical presentation & history of cholecystectomy were collected from the medical records. The pathologic findings were reviewed.

Results (if a Case Study enter NA)

We identified 4 women with an age range of 45-52 (mean=50). Three patients presented with abnormal uterine bleeding and one patient was admitted for sterilization. The time interval from cholecystectomy was 3-26 years (mean=18).Intra-operative findings were as follows: Case 1: blue-black 5 mm lesion located in the right ovary, Case 2: yellow-surface nodularity of left ovary and <1 cm white lesion in posterior cul- de sac, Case 3 two left ovarian cysts (0.8 and 1.5 cm), and Case 4 for sterilization showed a 0.3 cm. brown peritoneal lesion and unremarkable fallopian tubes. The histologic findings revealed bile pigment/crystals overlying the surfaces of the ovaries (3) peritoneum (1), & pelvis (1) with fibrosis and foreign-body giant cell reaction. The pathologic diagnosis was made in conjunction with prior history of cholecystectomy. Halls bilirubin stain was positive in 2/2 cases.

Conclusion

Pelvic cholelithiasis is an incidental finding in pre and post-menopausal women often involving the ovaries, peritoneum and pelvis. Intra-operatively, it could mimic endometriosis and pelvic mass. Histologic findings show bile pigment/crystals on serosal surface with fibrosis and foreign-body giant cell reaction. Familiarity with the histologic findings in conjunction with history of cholecystectomy is helpful in arriving at the correct diagnosis.

ALK rearranged renal cell carcinoma (ALK-RCC): a multi-institutional study of twelve cases with identification of novel partner genes CLIP1, KIF5B and KIAA1217

ALK rearranged renal cell carcinoma (ALK-RCC) has recently been included in 2016 WHO classification as a provisional entity. In this study, we describe 12 ALK-RCCs from 8 institutions, with detailed clinical, pathological, immunohistochemical (IHC), fluorescence in situ hybridization (FISH), and next generation sequencing (NGS) analyses. Patients' age ranged from 25 to 68 years (mean, 46.3 years). Seven patients were females and five were males (M:F = 1:1.4). Tumor size ranged from 17 to 70 mm (mean 31.5, median 25 mm). The pTNM stage included: pT1a (n = 7), pT1b (n = 1), and pT3a (n = 4). Follow-up was available for 9/12 patients (range: 2 to 153 months; mean 37.6 months); 8 patients were alive without disease and one was alive with distant metastases. The tumors demonstrated heterogeneous, 'difficult to classify' morphology in 10/12 cases, typically showing diverse architectural and cellular morphologies, including papillary, tubular, tubulocystic, solid, sarcomatoid (spindle cell), rhabdoid, signet-ring cell, and intracytoplasmic vacuoles, often set in a mucinous background. Of the remaining two tumors, one showed morphology resembling mucinous tubular and spindle cell renal cell carcinoma (MTSC RCC-like) and one was indistinguishable from metanephric adenoma. One additional case also showed a focal metanephric adenoma-like area, in an otherwise heterogeneous tumor. By IHC, all tumors were diffusely positive for ALK and PAX8. In both cases with metanephric adenoma-like features, WT1 and ALK were coexpressed. ALK rearrangement was identified in 9/11 tumors by FISH. ALK fusion partners were identified by NGS in all 12 cases, including the previously reported: STRN (n = 3), TPM3 (n = 3), EML4 (n = 2), and PLEKHA7 (n = 1), and also three novel fusion partners: CLIP1 (n = 1), KIF5B (n = 1), and KIAA1217 (n = 1). ALK-RCC represents a genetically distinct entity showing a heterogeneous histomorphology, expanded herein to include unreported metanephric adenoma-like and MTSC RCC-like variants. We advocate a routine ALK IHC screening for "unclassifiable RCCs" with heterogeneous features.

SUN-739 Next Generation AR Antagonists Increase Systemic Active Glucocorticoid Exposure by Altering Glucocorticoid Metabolism

Enzalutamide and apalutamide are potent next-generation androgen receptor (AR) antagonists used in metastatic and non-metastatic prostate cancer. Despite the increased survival benefits of these agents, resistance normally occurs and the disease transitions to its lethal form. We hypothesized that enzalutamide and apalutamide suppress 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2), which normally converts cortisol to cortisone, leading to elevated cortisol concentrations and increased ratio of active to inactive glucocorticoids. We measured cortisol and cortisol/cortisone ratio (substrate/product of 11β-HSD2) in serum using mass spectrometry before and 1 month on-treatment in 3 clinical trials: 1) neoadjuvant apalutamide + leuprolide (n=25) 2) enzalutamide +/- PROSTVAC for metastatic castration-resistant prostate cancer (n=54) and 3) enzalutamide +/- PROSTVAC for non-metastatic castration-sensitive prostate cancer (n=38 patients). Progression-free survival (PFS) was determined in the metastatic CRPC study of enzalutamide +/- PROSTVAC for those with glucocorticoid changes above and below the median. A statistically significant rise in cortisol concentration and cortisol/cortisone ratio with AR antagonist treatment occurred uniformly across all 3 clinical trials. For example, a rise in cortisol/cortisone ratio occurred in 23/25 (92%) patients (p < 0.001), 36/54 (67%) patients (p < 0.001), and 30/38 (79%) patients (p = 0.051), in the 3 respective trials. In the trial of enzalutamide +/- PROSTVAC for metastatic CRPC, high cortisol/cortisone ratio in the enzalutamide arm was associated with significantly improved PSA progression-free survival and radiographic progression-free survival. However, in the enzalutamide + PROSTVAC arm, the opposite trend was observed. In conclusion, treatment with enzalutamide or apalutamide increases systemic exposure to active glucocorticoids. These findings have potential consequences for immune suppression and the efficacy of treatment combinations using next-generation AR antagonists. On-treatment, glucocorticoid changes might serve as a pharmacodynamic biomarker.

Pancreatic tropism of metastatic renal cell carcinoma

Renal cell carcinoma (RCC) is characterized by a particularly broad metastatic swath, and, enigmatically, when the pancreas is a destination, the disease is associated with improved survival. Intrigued by this observation, we sought to characterize the clinical behavior, therapeutic implications, and underlying biology. While pancreatic metastases (PM) are infrequent, we identified 31 patients across 2 institutional cohorts and show that improved survival is independent of established prognostic variables, that these tumors are exquisitely sensitive to antiangiogenic agents and resistant to immune checkpoint inhibitors (ICIs), and that they are characterized by a distinctive biology. Primary tumors of patients with PM exhibited frequent PBRM1 mutations, 3p loss, and 5q amplification, along with a lower frequency of aggressive features such as BAP1 mutations and loss of 9p, 14q, and 4q. Gene expression analyses revealed constrained evolution with remarkable uniformity, reduced effector T cell gene signatures, and increased angiogenesis. Similar findings were observed histopathologically. Thus, RCC metastatic to the pancreas is characterized by indolent biology, heightened angiogenesis, and an uninflamed stroma, likely underlying its good prognosis, sensitivity to antiangiogenic therapies, and refractoriness to ICI. These data suggest that metastatic organotropism may be an indicator of a particular biology with prognostic and treatment implications for patients.

The effect of deep AR suppression with enzalutamide or apalutamide on endogenous glucocorticoids: Implications for adverse effects and development of combination therapies

17

Background: Metabolic consequences of potent AR suppression with enzalutamide and apalutamide are unresolved. Endocrine perturbations induced by potent AR antagonists may promote adverse effects and impinge on the potential efficacy of combination therapies, including for example, immunotherapies. We hypothesized that enzalutamide and apalutamide will block 11β-HSD2, the major enzyme that inactivates cortisol in peripheral tissues and results in increased systemic exposure to endogenous active glucocorticoids. We further hypothesized that AR is co-expressed with 11β-HSD2, suggesting a mechanism of suppression. Methods: Cortisol and cortisol/cortisone ratio (substrate/product of 11β-HSD2) were measured in serum using mass spectrometry before and on-treatment in 3 clinical trials: 1) neoadjuvant apalutamide + leuprolide 2) enzalutamide +/- PROSTVAC for metastatic castration-resistant prostate cancer 3) enzalutamide +/- PROSTVAC for non-metastatic castration-sensitive prostate cancer. AR and 11β-HSD2 expression were assessed in kidneys of 13 men and 9 women. Results: A rise in cortisol concentration and cortisol/cortisone ratio occurs uniformly across all 3 trials of potent AR antagonists. For example, a rise in cortisol/cortisone ratio occurred in 23/25 (92%) patients (p<0.001), 30/38 (79%) patients (p=0.051), and 36/64 (67%) patients (p<0.001), in the 3 respective trials. AR is only expressed alongside 11β-HSD2 in the kidneys of men but not women. Conclusions: Treatment with enzalutamide or apalutamide increases systemic exposure to active glucocorticoids. This effect is likely mediated by AR suppression of 11β-HSD2 in the kidney. These findings have potential consequences for immune suppression, the efficacy of treatment combinations using next-generation AR antagonists, and adverse effects of these drugs.

Deep androgen receptor suppression in prostate cancer exploits sexually dimorphic renal expression for systemic glucocorticoid exposure

BACKGROUND

Enzalutamide and apalutamide are potent next-generation androgen receptor (AR) antagonists used in metastatic and non-metastatic prostate cancer. Metabolic, hormonal and immunologic effects of deep AR suppression are unknown. We hypothesized that enzalutamide and apalutamide suppress 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2), which normally converts cortisol to cortisone, leading to elevated cortisol concentrations, increased ratio of active to inactive glucocorticoids and possibly suboptimal response to immunotherapy. On-treatment glucocorticoid changes might serve as an indicator of active glucocorticoid exposure and resultant adverse consequences.

PATIENTS AND METHODS

Human kidney tissues were stained for AR and 11β-HSD2 expression. Patients in three trials [neoadjuvant apalutamide plus leuprolide, enzalutamide ± PROSTVAC (recombinant poxvirus prostate-specific antigen vaccine) for metastatic castration-resistant prostate cancer (CRPC) and enzalutamide ± PROSTVAC for non-metastatic castration-sensitive prostate cancer] were analyzed for cortisol and its metabolites using liquid chromatography-mass spectrometry (LC-MS/MS). Progression-free survival was determined in the metastatic CRPC study of enzalutamide ± PROSTVAC for those with glucocorticoid changes above and below the median.

RESULTS

Concurrent AR and 11β-HSD2 expression occurs only in the kidneys of men. A statistically significant rise in cortisol concentration, cortisol/cortisone ratio and tetrahydrocortisol/tetrahydrocortisone ratio with AR antagonist treatment occurred uniformly across all three trials. In the trial of enzalutamide ± PROSTVAC for metastatic CRPC, high cortisol/cortisone ratio in the enzalutamide arm was associated with significantly improved progression-free survival. However, in the enzalutamide + PROSTVAC arm, the opposite trend was observed.

CONCLUSION

Enzalutamide and apalutamide treatment toggles renal 11β-HSD2 and significantly increases indicators of and exposure to biologically active glucocorticoids, which is associated with clinical outcomes.

MBOAT7-driven phosphatidylinositol remodeling promotes the progression of clear cell renal carcinoma

Objective

The most common kidney cancer, clear cell renal cell carcinoma (ccRCC), is closely associated with obesity. The “clear cell” variant of RCC gets its name from the large lipid droplets that accumulate in the tumor cells. Although renal lipid metabolism is altered in ccRCC, the mechanisms and lipids driving this are not well understood.

Methods

We used shotgun lipidomics in human ccRCC tumors and matched normal adjacent renal tissue. To assess MBOAT7s gene expression across tumor severity, we examined histologically graded human ccRCC samples. We then utilized genome editing in ccRCC cell lines to understand the role of MBOAT7 in ccRCC progression.

Results

We identified a lipid signature for ccRCC that includes an increase in arachidonic acid-enriched phosphatidylinositols (AA-PI). In parallel, we found that ccRCC tumors have increased expression of acyltransferase enzyme membrane bound O-acyltransferase domain containing 7 (MBOAT7) that contributes to AA-PI synthesis. In ccRCC patients, MBOAT7 expression increases with tumor grade, and increased MBOAT7 expression correlates with poor survival. Genetic deletion of MBOAT7 in ccRCC cells decreases proliferation and induces cell cycle arrest, and MBOAT7^−/− cells fail to form tumors in vivo. RNAseq of MBOAT7^−/− cells identified alterations in cell migration and extracellular matrix organization that were functionally validated in migration assays.

Conclusions

This study highlights the accumulation of AA-PI in ccRCC and demonstrates a novel way to decrease the AA-PI pool in ccRCC by limiting MBOAT7. Our data reveal that metastatic ccRCC is associated with altered AA-PI metabolism and identify MBOAT7 as a novel target in advanced ccRCC.

Unraveling the molecular profile underpinning pancreatic tropisms in metastatic clear cell renal cell carcinoma

e16096

Background: The tropism of cancer metastases is poorly understood yet holds prognostic value. Clear cell renal cell carcinoma (ccRCC) exhibits a broad pattern of metastases, making it an optimal model to study organotropism. Notably, when ccRCC metastasizes to the pancreas (PM) independently of other sites, it is associated with favorable outcomes in patients for unclear reasons. Here, we comprehensively analyzed the clinical and molecular profile of patients with PM. Methods: RCC patients with PM from UTSW and Cleveland Clinic were identified. Clinicopathologic data and oncologic outcomes were analyzed. Whole exome sequencing (WES), RNAseq, and histologic assessment of primary and metastatic tumors from PM patients were conducted. Results: 31 RCC patients with PM were identified. We observed remarkably favorable outcomes in our PM cohort, with a median overall survival (OS) of 10.7 years from metastatic diagnosis and a long latency between initial diagnosis and development of metastasis (median 69 months in patients who were non-metastatic at diagnosis). OS was independent of both metastatic tumor burden and known IMDC prognostic factors. We discovered that tumors from PM patients were markedly uniform and clustered together by gene expression analysis. WES and DNA copy number analyses revealed a high frequency of VHL and PBRM1 mutations, 3p loss, and 5q amplification, along with a lower frequency of 9p, 14q and 4q losses and BAP1 mutations, characteristic of indolent ccRCC. Furthermore, the genomic and histologic features of tumors from patients with PM can be recapitulated in patient-derived xenograft models. Conclusions: To our knowledge, this is the first report to unravel molecular determinants of organotropism, and we highlight that organotropism can be an independent prognostic factor. Understanding tumor heterogeneity may help refine prognostic models for metastatic RCC and hold implications for improved personalization of therapy.

Evaluation of T cell infiltration in matched biopsy and nephrectomy samples in renal cell carcinoma

T cell infiltration in tumors has been investigated as a biomarker of response to checkpoint inhibitors. Neo-adjuvant studies in renal cell carcinoma (RCC) may provide a unique opportunity to compare T cell infiltration in a pretreatment renal mass biopsy to a posttreatment nephrectomy specimen, and thus evaluate the effects of immune checkpoint inhibitors. However, there are no data regarding the association of T cell infiltration in matched biopsy and nephrectomy samples without intervening treatment. Understanding this association will inform investigation of this potential biomarker in future studies.Matched biopsy and nephrectomy samples (without intervening systemic therapy) were identified from patients with nonmetastatic RCC. Selected tissue sections from biopsy and nephrectomy samples were reviewed and marked for intratumoral lymphocytes by a pathologist. Immunohistochemistry (IHC) was utilized to stain for T cell markers (CD3, CD4, and CD8). Intratumoral staining was then quantified in the tissue sections as counts per total tumor area surveyed. Spearman correlation (r) was used to measure associations.Thirty matched pairs were investigated. The median interval between biopsy and nephrectomy was 2.8 (0.2-87.7) months. Clear cell was the most common histology (29/30; 97%). There was a statistically significant positive correlation between the frequency of CD3 and CD8 T cells between matched biopsy and nephrectomy samples (r = 0.39; P = .036 and r = 0.38; P = .041, respectively).The frequencies of CD8+ T cells in matched biopsy and nephrectomy samples in RCC in the absence of intervening treatment have been characterized and show a positive correlation between matched biopsy and nephrectomy samples.

T cell infiltration (TCI) in matched renal biopsy (bx) and nephrectomy (nx) samples in renal cell carcinoma (RCC)

4587

Background: TCI in tumors has been investigated as a biomarker of response to checkpoint inhibitors. A neo-adjuvant trial of checkpoint inhibition in locally-advanced RCC is ongoing at Cleveland Clinic, where TCI in pre-treatment renal mass bx will be compared to post-treatment nx specimens. However, there are no data regarding the association of TCI in matched bx and nx samples without intervening treatment. Understanding this association will enable further study of this potential biomarker in future studies. Methods: Matched bx and nx samples (without intervening systemic therapy) were identified from patients with non-metastatic RCC. Selected tissue sections from bx and nx samples were reviewed, and marked for intra-tumoral lymphocytes by the Pathologist. Immunohistochemistry (IHC) was utilized to stain these selected tissue sections for T cell markers (CD3, CD4 and CD8), and additional immune markers including PD-1, PDL-1 and CD11b. Intra-tumoral staining was then quantified in the pre-marked tissue sections as counts per total tumor area surveyed. Spearman correlation (ρ) was used to measure the strength of association. Results: 30 matched pairs were investigated. The median interval between bx and nx was 2.8 (0.2-87.7) months. Clear cell was the most common histology (29/30; 97%). There was a positive correlation between the frequency of CD8+T cells between matched bx and nx samples (ρ= 0.39; p=0.03). CD3, CD4 and CD11b did not show significant correlation. (Table) PD-1 (bx 4/29, nx 16/29) and PDL-1 (bx 5/28, nx 10/28) expression was positive in the minority of samples. Conclusions: Bx material can potentially be used to assess the degree of CD8+ TCI in RCC nx samples. However the utility of bx evaluation for CD4+TCI and expression of PD-1, PDL-1 and CD11b requires further study. [Table: see text]

T cell infiltration in matched renal biopsy (bx) and nephrectomy (nx) samples in renal cell carcinoma (RCC)

472

Background: T cell infiltration in tumors has been investigated as a biomarker of response to checkpoint inhibitors. A neo-adjuvant trial of checkpoint inhibition in locally-advanced RCC is ongoing at Cleveland Clinic, where T cell infiltration in pre-treatment renal mass bx will be compared to post-treatment nx specimens. However, there are no data regarding the association of T cell infiltration in matched bx and nx samples without intervening treatment. Understanding this association will enable further study of this potential biomarker in future neo-adjuvant studies. Methods: Matched bx and nx samples (without intervening systemic therapy) were identified from patients with non-metastatic RCC. Demographic and pathological data were collected from chart review. Selected tissue sections from bx and nx samples of each patient were reviewed, and marked for tumor and intra-tumoral lymphocytes by the pathologist. Immunohistochemistry (IHC) was utilized to stain these selected tissue sections for T cell markers (CD3, CD4 and CD8). Intra-tumoral T cells were then quantified in the pre-marked tissue sections as counts per total tumor area surveyed, using Image-Pro Plus (Media Cybernetics, Inc.). Spearman correlation (ρ) was used to measure the strength of association of T cell infiltration between matched samples. Results: 30 matched pairs were investigated. The median interval between bx and nx was 2.8 (0.2-87.7) months. Clear cell was the most common histology (29/30; 97%). 15/30 (50%) had grade 3-4 tumors, 2/19 (11%) patients had sarcomatoid features, 7/25 (29%) had necrosis, and 8/28 (29%) had lymphovascular invasion. We found a positive correlation between the frequencies of CD8+ T cells between matched bx and nx samples (ρ= 0.39; p=0.03). CD3+ and CD4+T cells did not show significant correlation. (Table) Conclusions: Bx material can be used to accurately assess the degree of CD8+T cell infiltration in RCC. [Table: see text]

Sunitinib's effect on tumor infiltration of CD8 T cells in renal cell carcinoma (RCC) and modulation of their function by altering VEGF-induced upregulation of PD1 expression

591

Background: The effect of VEGF inhibitors such as sunitinib to modulate RCC tumor microenvironment and the effect on immunotherapy using checkpoint inhibitors is unknown and of clinical interest. Methods: Immune infiltrate in tissue sections from clear cell renal cell carcinomas (ccRCC) (n = 13) treated with sunitinib in the neoadjuvant setting were compared to that of untreated RCC patients with localized disease (n = 15). Immune infiltrate was scored in H&E stained tissue sections. Infiltrates were further characterized by IHC using antibodies against CD4 (Novocastra NCL-CD4-1F6 clone 1F6), CD8 (BiogeneX MU422-UC clone 1A5) or PD1 (Abcam ab52587 clone EPR4877). Intensity of staining was quantified using a Leica microscope equipped with a Retiga SRV camera. Scanned images of multiple tumor fields were analyzed using ImagePro Plus software. For pre-clinical studies, Balb/c mice bearing Renca tumors (RCC) were treated with sunitinib (40mg/kg) daily for 14 days, and tumors were dissociated and analyzed for CD8 and CD4 infiltrate by FACS analysis. Results: Qualitative analysis showed a more prominent accumulation of lymphocytes in tumor sections of patients receiving sunitinib. Quantitative analysis of these infiltrates revealed higher levels of CD8+ T cells in sunitinib treated patients (p = 0.04). By contrast, sunitinib treatment was associated with a reduction of intratumoral expression of PD1. Preclinical studies in the Renca model also showed an increase in the frequency of tumor infiltrating CD8+ T cells following sunitinib treatment. Remarkably, a higher fraction of these tumor infiltrating CD8 T cells were found to co-express the activation marker of cytotoxic effector cells (CD107a) when compared to untreated mice. Conclusions: These findings suggest that sunitinib not only promotes the accumulation of CD8+ T cells within the tumors, but also affects their activity by modulating PD1 expression and enhancing cytotoxic function.

Association of PD-1 and PD-L1 protein expression in matched primary and metastatic renal cell carcinoma tumors

418

Background: Therapy targeting programmed death (PD)-1 and PD-L1 proteins has activity in metastatic renal cell carcinoma (mRCC). Expression of these proteins on tumor and infiltrating immune cells is associated with a higher response to drugs inhibiting this pathway. However, these associations have been made based on primary tumor expression, while therapy is directed against metastatic deposits. Methods: Patients with mRCC and metastases (all clear cell; 3 with sarcomatoid changes) who had undergone resection of both the primary and at least one metastatic tumor were included. Samples were evaluated for PD-1 and PD-L1 expression by immunohistochemistry using anti-PD-1 clone NAT105 and Merck proprietary anti-PD-L1 clone 22C3. Stained sections were scored for PD-1 and PD-L1 using a semi-quantitative 0 to 5 scale (0 = negative, 1 = rare, 2 = low, 3 = moderate, 4= high, 5 = very high). PD-1 expression was limited to cells with lymphoid morphology, PD-L1 expression was evaluated for both tumor and non-tumor (inflammatory, endothelial) cells. Linear regression analysis was performed to assess significance of correlations. Results: Fifty matched primary and metastatic RCC tissue sets were analyzed with 48 evaluable matched pairs. PD-1 score greater than 3 (considered positive) was detected in 9 primary tumors (18%) and 9 metastatic sites (18%). PD-L1 score greater than 3 was detected in 9 primary tumors (18%) and 12 metastatic sites (24%). There was a correlation between PD-1 scores for primary and metastatic pairs (R2=0.194; p<0.002) and between PD-L1 scores for primary and metastatic pairs (R2=0.319; p<0.0001). There was an association between PD-1 score and PD-L1 score for primary tumors (R2=0.513; p<0.0001) and for metastatic sites (R2=0.449; p<0.0001). For PD-1 score, there were 10 pairs (21%) in which either the primary or metastatic site score was ≥3, but the matched pair was < 3. For PD-L1 score, there were 9 pairs (19%) in which either the primary or metastatic site score was ≥3, but the matched pair was < 3. Conclusions: The expression of PD1 and PD-L1 in primary clear cell RCC tumors is correlated with metastatic site expression, although there are a substantial percentage of tumors with discordance.

Succinate dehydrogenase (SDH)-deficient renal carcinoma: a morphologically distinct entity: a clinicopathologic series of 36 tumors from 27 patients

Succinate dehydrogenase (SDH)-deficient renal carcinoma has been accepted as a provisional entity in the 2013 International Society of Urological Pathology Vancouver Classification. To further define its morphologic and clinical features, we studied a multi-institutional cohort of 36 SDH-deficient renal carcinomas from 27 patients, including 21 previously unreported cases. We estimate that 0.05% to 0.2% of all renal carcinomas are SDH deficient. Mean patient age at presentation was 37 years (range, 14 to 76 y), with a slight male predominance (M:F=1.7:1). Bilateral tumors were observed in 26% of patients. Thirty-four (94%) tumors demonstrated the previously reported morphology at least focally, which included: solid or focally cystic growth, uniform cytology with eosinophilic flocculent cytoplasm, intracytoplasmic vacuolations and inclusions, and round to oval low-grade nuclei. All 17 patients who underwent genetic testing for mutation in the SDH subunits demonstrated germline mutations (16 in SDHB and 1 in SDHC). Nine of 27 (33%) patients developed metastatic disease, 2 of them after prolonged follow-up (5.5 and 30 y). Seven of 10 patients (70%) with high-grade nuclei metastasized as did all 4 patients with coagulative necrosis. Two of 17 (12%) patients with low-grade nuclei metastasized, and both had unbiopsied contralateral tumors, which may have been the origin of the metastatic disease. In conclusion, SDH-deficient renal carcinoma is a rare and unique type of renal carcinoma, exhibiting stereotypical morphologic features in the great majority of cases and showing a strong relationship with SDH germline mutation. Although this tumor may undergo dedifferentiation and metastasize, sometimes after a prolonged delay, metastatic disease is rare in the absence of high-grade nuclear atypia or coagulative necrosis.