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Supplemental Figure Legend

Supplemental Figure 1. Tumor infiltrating Treg; Supplemental Figure 2. Treg and IFN�-CD8.

Purpose: On the basis of preclinical data suggesting that the class I selective HDAC inhibitor entinostat exerts a synergistic antitumor effect in combination with high-dose IL2 in a renal cell carcinoma model by downregulating Foxp3 expression and function of regulatory T cells (Treg), we conducted a phase I/II clinical study with entinostat and high-dose IL2 in patients with metastatic clear cell renal cell carcinoma (ccRCC).Experimental Design: Clear cell histology, no prior treatments, and being sufficiently fit to receive high-dose IL2 were the main eligibility criteria. The phase I portion consisted of two dose levels of entinostat (3 and 5 mg, orally every 14 days) and a fixed standard dose of IL2 (600,000 U/kg i.v.). Each cycle was 85 days. The primary endpoint was objective response rate and toxicity. Secondary endpoints included progression-free survival and overall survival.Results: Forty-seven patients were enrolled. At a median follow-up of 21.9 months, the objective response rate was 37% [95% confidence interval (CI), 22%–53%], the median progression-free survival was 13.8 months (95% CI, 6.0–18.8), and the median overall survival was 65.3 months (95% CI, 52.6.-65.3). The most common grade 3/4 toxicities were hypophosphatemia (16%), lymphopenia (15%), and hypocalcemia (7%), and all were transient. Decreased Tregs were observed following treatment with entinostat, and lower numbers were associated with response (P = 0.03).Conclusions: This trial suggests a promising clinical activity for entinostat in combination with high-dose IL2 in ccRCC patients and provides the first example of an epigenetic agent being rationally combined with immunotherapy. Clin Cancer Res; 23(23); 7199–208. ©2017 AACR.

Supplementary Table S1- Number of patients with 1-4 and {greater than or equal to}5 CTCs per 7.5mL of whole blood at baseline, and at 3, 6 and 12 months. Supplementary Table S2- Biochemical markers of bone turnover and bone mineral density (BMD).

Supplementary Data from Treatment-free Survival after Immune Checkpoint Inhibitor Therapy versus Targeted Therapy for Advanced Renal Cell Carcinoma: 42-Month Results of the CheckMate 214 Trial

Pembrolizumab plus axitinib improved efficacy over sunitinib in treatment-naive advanced renal cell carcinoma in the KEYNOTE-426 (NCT02853331) study. However, a relatively high incidence of grade 3/4 aminotransferase elevations was observed.To further characterize treatment-emergent aminotransferase elevations in patients treated with pembrolizumab-axitinib.Patients enrolled in KEYNOTE-426 were included in this study.Three Standardized MedDRA Queries for potential hepatic disorders were used to identify patients for the hepatic event analysis subpopulation (HEAS). Alanine aminotransferase events were characterized for time to onset, time to recovery, corticosteroid use, and rechallenge with study treatment(s).The HEAS comprised 189/429 (44%) pembrolizumab-axitinib patients and 128/425 (30%) sunitinib patients. Grade 3/4 hepatic adverse events were more common in the combination arm: 22% (94/429) versus 7% (29/425); 3% (13/429) discontinued the combination due to hepatic adverse events. In the pembrolizumab-axitinib arm, 125/426 patients (29%) had alanine aminotransferase (ALT) ≥3× upper limit of normal (ULN), with median time to onset of 84 d (range, 7-840 d). Among patients with ALT ≥3× ULN, 120/125 (96%) recovered to3× ULN following study treatment interruption/discontinuation, with a median time to recovery of 15 d (3-176 d): 68/120 (57%) received corticosteroids. One hundred patients were rechallenged with one or both study treatment(s): 45/100 (45%) had ALT ≥3× ULN recurrence, and all 45 recovered to ALT3× ULN following study treatment interruption/discontinuation. No fatal hepatic events occurred.A higher incidence of grade 3/4 aminotransferase elevations occurs with pembrolizumab-axitinib. These events should be carefully evaluated and managed with prompt study treatment interruption or discontinuation, with or without corticosteroid treatment. The decision to rechallenge with one or both drugs should be based on severity of event and thorough causality assessment.Renal cell carcinoma patients receiving pembrolizumab-axitinib are at a higher risk of liver enzyme elevations, which could be reversed with appropriate management.

Neoadjuvant immune checkpoint blockade represents a novel approach for potentially decreasing the risk of recurrence in patients with nonmetastatic renal cell carcinoma (RCC). In this early phase clincal tiral, we evaluated the safety and tolerability of neoadjuvant treatment with the programmed cell death protein 1 (PD-1) inhibitor nivolumab in patients with nonmetastatic high-risk RCC. Nonprimary endpoints included objective radiographic tumor response rate, immune-related pathologic response rate, quality of life alterations, and metastasis-free and overall survival. In total, 17 patients were enrolled in this study and underwent surgery without a delay after receiving three every-2-wk doses of neoadjuvant nivolumab. Adverse events (AEs) of any grade occurred in 14 (82.4%) patients, with two (11.8%) experiencing grade 3 events. Ten (58.8%) patients experienced an AE of any grade potentially attributable to nivolumab (all grade 1–2), and no grade 4–5 AEs occurred regardless of treatment attribution. The most common AEs were grade 1 fatigue (41.2%), grade 1 pruritis (29.4%), and grade 1 rash (29.4%). All evaluable patients had stable disease as per established radiographic criteria, with one (6.7%) demonstrating features of an immune-related pathologic response. Quality of life remained stable during treatment, with improvements relative to baseline noted at ≥6 mo postoperatively. Metastasis-free survival and overall survival were 85.1% and 100% at 2 yr, respectively. Patient summary In this study, we evaluated the safety and tolerability of preoperative administration of three doses of the immune checkpoint inhibitor nivolumab in patients with clinically localized high-risk renal cell carcinoma. We demonstrated the safety of this approach and found that, although most patients will not experience a radiographic response to treatment, a subset may have features of an immune-related pathologic response.

Close to 74,000 cases of renal cell carcinoma (RCC) are diagnosed each year in the United States. The past 2 decades have shown great developments in surgical techniques, targeted therapy and immunotherapy agents, and longer complete response rates. However, without a global cure, there is still room for further advancement in improving patient care in this space. To address some of the gaps restricting this progress, the Kidney Cancer Association brought together a group of 27 specialists across the areas of clinical care, research, industry, and advocacy at the inaugural "Think Tank: Coalition for a Cure" session. Topics addressed included screening, imaging, rarer RCC subtypes, combination drug therapy options, and patient response. This commentary summarizes the discussion of these topics and their respective clinical challenges, along with a proposal of projects for collaboration in overcoming those needs and making a greater impact on care for patients with RCC moving forward.

Background Systemic therapy (ST) can be deferred in patients who have metastatic renal cell carcinoma (mRCC) and slow-growing metastases. Currently, this subset of patients managed with active surveillance (AS) is not well described in the literature. Methods This was a prospective observational study of patients with mRCC across 46 US community and academic centers. The objective was to describe baseline characteristics and demographics of patients with mRCC initially managed by AS, reasons for AS, and patient outcomes. Descriptive statistics were used to characterize demographics, baseline characteristics, and patient-related outcomes. Wilcoxon 2-sample rank-sum tests and χ2 tests were used to assess differences between ST and AS cohorts in continuous and categorical variables, respectively. Kaplan-Meier survival curves were used to assess survival. Results Of 504 patients, mRCC was initially managed by AS (n = 143) or ST (n = 305); 56 patients were excluded from the analysis. Disease was present in 69% of patients who received AS, whereas the remaining 31% had no evidence of disease. At data cutoff, 72 of 143 patients (50%) in the AS cohort had not received ST. The median overall survival was not reached (95% CI, 122 months to not estimable) in patients who received AS versus 30 months (95% CI, 25-44 months) in those who received ST. Quality of life at baseline was significantly better in patients who were managed with AS versus ST. Conclusions AS occurs frequently (32%) in real-world clinical practice and appears to be a safe and appropriate alternative to immediate ST in selected patients.

PURPOSE Immune checkpoint inhibitors (ICIs) are standard therapy in metastatic renal cell carcinoma (RCC). The safety and activity of the combination of ipilimumab and nivolumab in patients who have received prior ICI targeting the programmed death 1 (PD-1) pathway remains unknown. We evaluated ipilimumab and nivolumab in patients with metastatic RCC after prior treatment with anti–PD-1 pathway–targeted therapy. PATIENTS AND METHODS Patients with metastatic RCC who received prior anti–PD-1 pathway-targeted therapy and subsequently received ipilimumab and nivolumab were reviewed. Objective response rate and progression-free survival per investigator assessment were recorded. Toxicity of ipilimumab and nivolumab was also assessed. RESULTS Forty-five patients with metastatic RCC were included. All patients (100%) received prior ICIs targeting the PD-1 pathway. The median age was 62 years (range, 21-82 years). At a median follow-up of 12 months, the objective response rate to ipilimumab and nivolumab was 20%. The median progression-free survival while on ipilimumab and nivolumab was 4 months (range, 0.8-19 months). Immune-related adverse events (irAEs) of any grade with ipilimumab and nivolumab were recorded in 29 (64%) of the 45 patients; grade 3 irAEs were recorded in 6 (13%) of the 45 patients. CONCLUSION Ipilimumab and nivolumab demonstrated antitumor activity with acceptable toxicity in patients with metastatic RCC who had prior treatment with checkpoint inhibition.

Background: CheckMate 025 has shown superior efficacy for nivolumab over everolimus in patients with advanced renal cell carcinoma (aRCC) along with improved safety and tolerability. This analysis assesses the long-term clinical benefits of nivolumab versus everolimus. Methods: The randomized, open-label, phase 3 CheckMate 025 trial (NCT01668784) included patients with clear cell aRCC previously treated with 1 or 2 antiangiogenic regimens. Patients were randomized to nivolumab (3 mg/kg every 2 weeks) or everolimus (10 mg once a day) until progression or unacceptable toxicity. The primary endpoint was overall survival (OS). The secondary endpoints were the confirmed objective response rate (ORR), progression-free survival (PFS), safety, and health-related quality of life (HRQOL). Results: Eight hundred twenty-one patients were randomized to nivolumab (n = 410) or everolimus (n = 411); 803 patients were treated (406 with nivolumab and 397 with everolimus). With a minimum follow-up of 64 months (median, 72 months), nivolumab maintained an OS benefit in comparison with everolimus (median, 25.8 months [95% CI, 22.2-29.8 months] vs 19.7 months [95% CI, 17.6-22.1 months]; hazard ratio [HR], 0.73; 95% CI, 0.62-0.85) with 5-year OS probabilities of 26% and 18%, respectively. ORR was higher with nivolumab (94 of 410 [23%] vs 17 of 411 [4%]; P

Kidney cancer is one of the 10 most common cancers both in the United States and worldwide. Until this year, there had not previously been a conference focused on translational studies in the broad and heterogeneous group of kidney cancers. Therefore, a group of researchers, clinicians, and patient advocates dedicated to renal cell carcinoma launched the Kidney Cancer Research Summit (KCRS) to spur collaboration and further therapeutic advances in these tumors. This commentary aims to summarize the oral presentations and serve as a record for future iterations of this meeting. The KCRS sessions addressed the tumor microenvironment, novel methods of drug delivery, single cell sequencing strategies, novel immune checkpoint blockade and cellular therapies, predictive biomarkers, and rare variants of kidney cancers. In addition, the meeting included 2 sessions to promote scientific mentoring and kidney cancer research collaborations. A subsequent KCRS will be planned for the fall of 2020.

PURPOSE: The time it takes a performing site to activate a clinical trial can directly affect the ability to provide innovative and state-of-the-art care to patients. We sought to understand the process of activating an oncology clinical trial at a matrix National Cancer Institute–designated comprehensive cancer center. METHODS: A multidisciplinary team of stakeholders within the cancer center, university, and affiliate hospitals held a retreat to map out the process of activating a clinical trial. We applied classical quality improvement and Six Sigma methodology to determine bottlenecks and non–value-added time in activating a clinical trial. During this process, attention was paid to time to pass through each step, and perceived barriers and bottlenecks were identified through group discussions. RESULTS: The process map identified 66 steps with 12 decision points to activate a new clinical trial. The following two steps were instituted first: allow parallel scientific committee and institutional review board (IRB) review and allow the clinical research coordination committee, a group that determines university interest and feasibility, to review protocols independent of the IRB and scientific committee approval. The clinical research coordination committee continues to track the activation time, and this framework is used to identify additional improvement steps. CONCLUSION: By applying quality improvement methodologies and Six Sigma principles, we were able to identify redundancies in the process to activate a clinical trial. This allowed us to redesign the process of activating a clinical trial at a matrix comprehensive cancer center. More importantly, the process map provides a framework to maintain these gains and implement additional changes and serves as an example to deploy across the campus and at other similar institutions.

Background: Conditional survival estimates provide critical prognostic information for patients with advanced renal cell carcinoma (aRCC). Efficacy, safety, and conditional survival outcomes were assessed in CheckMate 214 (ClinicalTrials.gov identifier NCT02231749) with a minimum follow-up of 5 years. Methods: Patients with untreated aRCC were randomized to receive nivolumab (NIVO) (3 mg/kg) plus ipilimumab (IPI) (1 mg/kg) every 3 weeks for 4 cycles, then either NIVO monotherapy or sunitinib (SUN) (50 mg) daily (four 6-week cycles). Efficacy was assessed in intent-to-treat, International Metastatic Renal Cell Carcinoma Database Consortium intermediate-risk/poor-risk, and favorable-risk populations. Conditional survival outcomes (the probability of remaining alive, progression free, or in response 2 years beyond a specified landmark) were analyzed. Results: The median follow-up was 67.7 months; overall survival (median, 55.7 vs 38.4 months; hazard ratio, 0.72), progression-free survival (median, 12.3 vs 12.3 months; hazard ratio, 0.86), and objective response (39.3% vs 32.4%) benefits were maintained with NIVO+IPI versus SUN, respectively, in intent-to-treat patients (N = 550 vs 546). Point estimates for 2-year conditional overall survival beyond the 3-year landmark were higher with NIVO+IPI versus SUN (intent-to-treat patients, 81% vs 72%; intermediate-risk/poor-risk patients, 79% vs 72%; favorable-risk patients, 85% vs 72%). Conditional progression-free survival and response point estimates were also higher beyond 3 years with NIVO+IPI. Point estimates for conditional overall survival were higher or remained steady at each subsequent year of survival with NIVO+IPI in patients stratified by tumor programmed death ligand 1 expression, grade ≥3 immune-mediated adverse event experience, body mass index, and age. Conclusions: Durable clinical benefits were observed with NIVO+IPI versus SUN at 5 years, the longest phase 3 follow-up for a first-line checkpoint inhibitor-based combination in patients with aRCC. Conditional estimates indicate that most patients who remained alive or in response with NIVO+IPI at 3 years remained so at 5 years.

708 Background: Novel perioperative strategies are needed to reduce recurrence rates in patients undergoing nephrectomy for high-risk, non-metastatic clear cell renal cell carcinoma (ccRCC). We sought to (1) elucidate the effects of PD-1 inhibition on primary tumor-infiltrating and circulating immune cell populations in ccRCC and (2) correlate tumor microenvironment and circulating immune cell compositions with response to anti-PD-1 therapy. Methods: We conducted a prospective, phase I trial of neoadjuvant nivolumab prior to nephrectomy in 15 evaluable patients with non-metastatic ccRCC. We leveraged tissue from this cohort to elucidate the effects of PD-1 inhibition on immune cell populations in ccRCC and correlate the evolving immune milieu with anti-PD-1 response using fluorescence-activated cell sorting, bulk RNA sequencing with protein activity inference, and enzyme-linked immunosorbent assay for circulating cytokines. Results: We found that nivolumab durably promotes a pro-inflammatory state within the primary tumor, as evidenced by a sustained increase in the effector T cell phenotype and decreased representation of regulatory T cell subsets. Baseline immune infiltration within the primary tumor including T effector and myeloid enrichment along with angiogenic depletion correlates with nivolumab responsiveness. Nivolumab increases CTLA-4 expression in the primary tumor, and subsequent nephrectomy increases circulating concentrations of sPD-L1, sPD-L3 (sB7-H3), and s4-1BB. Conclusions: Our findings form the basis to consider neoadjuvant immune checkpoint inhibition (ICI) for high-risk ccRCC while the tumor remains in situ and provide the rationale for perioperative strategies of novel ICI combinations. Clinical trial information: NCT02575222 .

666 Background: Activation of the GAS6/AXL pathway promotes tumor cell proliferation; high levels of GAS6 and AXL have been associated with drug resistance and decreased survival. Batiraxcept is an ultra-high affinity decoy protein that captures GAS6, preventing it from activating AXL signaling. Serum soluble AXL (sAXL)/GAS6 ratio correlates with response to batiraxcept in advanced ovarian cancer. Batiraxcept in combination with cabozantinib is being evaluated in patients (pts) with metastatic clear cell renal cell carcinoma (ccRCC) in this study. Prior studies of cabozantinib in similar pt populations have shown an overall response rate (ORR) ranging from 15 – 32.5% and progression-free survival (PFS) from 3.7-7.2 months (mo). Methods: Key eligibility criteria include previously treated ccRCC pts, excluding prior cabozantinib. Objectives were to determine the safety of batiraxcept plus cabozantinib 60 mg, the recommended phase 2 dose (RP2D), ORR, PFS, duration of response. Correlative endpoints included assessment of baseline serum sAXL/GAS6 with ORR and PFS. Results: In Phase 1b (P1b), 26 pts received at least one dose of batiraxcept with cabozantinib (16 pts - 15 mg/kg; 10 pts - 20 mg/kg). Median age was 60 (range 40-81), male 85% (n=22), IMDC intermediate/poor risk 77% (n=20). All pts received prior immuno-oncology (IO) therapy, 54% (n=14) also received VEGF-TKI; 85% (n=22) received 1 to 2 prior lines of therapy (range 1-6). Median follow-up time was 11.6 mo (range 3.7-18). The RP2D is 15 mg/kg. Related adverse events (AE) any grade and grade ≥ 3 were 100% and 39% (n=10), respectively. Cabozantinib dose reductions occurred in 54% (n=14). AEs of special interest were grade 1 or 2 infusion related reactions, 27% (n=7). Batiraxcept was discontinued due to disease progression 62% (n=16) or toxicity 12% (n=3). The table shows P1b efficacy, ORR of 42%, median PFS of 9.3 mo, and DCR of 84%. Twenty (77%) pts had high baseline sAXL/GAS6 levels; ORR was 55% (11/20) with mPFS of 9.3 mo, compared to 0% ORR and mPFS 6.4 mo in the low sAXL/GAS6 pts. Conclusions: Batiraxcept was well tolerated when combined with cabozantinib. No new safety signals were noted. Efficacy for the combination is encouraging compared to historical cabozantinib monotherapy data. Higher GAS6 levels were predictive for treatment response. The P2 accrual is complete and efficacy data are maturing. A P3 trial plans to evaluate the efficacy in ccRCC patients who have progressed on IO-based and VEGF-TKI therapies. Clinical trial information: NCT04300140 . [Table: see text]

604 Background: Treatment with immunotherapy can be associated with prolonged disease control after discontinuation without the need for further anticancer therapy. Toxicity from therapy can also persist after cessation. TFS with and without toxicity can characterize survival time. Significant TFS was reported for CheckMate 067 trial in pts with metastatic melanoma (Regan et al JITC 2021) and CheckMate 214 trial for pts with aRCC (Regan et al CCR 2021), but treatment was often halted for toxicity rather than a pre-defined treatment endpoint. We therefore sought to assess TFS in the HCRN GU16 260 trial, which was designed to reduce toxicity and to cap immunotherapy duration (Atkins et al JCO 2022). Methods: Data were analyzed from 128 patients (pts) with clear-cell aRCC treated with first-line nivolumab (NIVO) monotherapy for up to 2 years. As part of the protocol, salvage nivolumab/ipilimumab (NIVO/IPI) for up to 1 year was provided to eligible patients with disease progression at any point or stable disease at 48 weeks (28% of pts). TFS was defined as the area between Kaplan-Meier curves for time from registration to protocol therapy cessation and for time from registration to subsequent therapy initiation or death, estimated from 36-month (mo) mean times. The time on treatment or off treatment with grade 3+ treatment-related adverse events (TRAEs) was also captured. Results: At 36 mos from enrollment, 68.3% of pts were alive: 96.8% of IMDC favorable-risk (FAV) pts and 56.6% of those with intermediate/poor-risk (I/P), respectively. The 36-mo mean time on protocol therapy was 11.5 mos (16.0 mos for FAV pts and 9.6 mos for I/P pts). The 36-mo mean TFS for the whole population was 9.4 mos. For FAV pts the mean TFS was 12.9 mos, of which TFS with grade 3+ TRAEs was 1.5 mos. For I/P pts, the mean TFS was 8.0 mos, of which TFS with grade 3+ TRAEs was 1.0 mos. At 36 mos, 65.6% of FAV pts and 27.1% of I/P pts were alive and second-line treatment-free. Conclusions: NIVO monotherapy with salvage NIVO/IPI in non-responders is an active treatment approach in treatment-naïve pts with aRCC and results in substantial TFS and toxicity-free TFS. TFS was particularly noted in pts with FAV disease, further supporting the use of an immunotherapy-only regimen in this population. Clinical trial information: NCT03117309 . [Table: see text]

698 Background: Nivolumab (nivo) monotherapy demonstrated anti-tumor activity in treatment-naïve renal cell carcinoma (RCC) in Part A of HCRN GU16-260 across all IMDC groups and in multiple histologies. Patient tumor samples were collected to characterize the tumor-immune microenvironmental (TME) determinants of effective anti-tumor immunity with nivo. Methods: Eligible patients (with clear cell or non-clear cell histology) underwent tumor biopsy prior to and/or at resistance to nivo monotherapy. Fresh tissue fragments were cryopreserved locally and centrally processed to extract viable single-cells from the RCC TME. Single-cell RNA-sequencing (scRNA-seq) and T cell receptor (TCR)-sequencing (scTCR-seq) was performed on all tumor samples. Gene expression signatures discovered through scRNA-seq were used to interrogate previously published bulk transcriptomic data from the CheckMate-009/010/025 trials of nivo in the treatment-refractory setting. Results: In total, 72,730 viable single-cells (56,900 immune and 15,830 tumor or stromal cells) were sequenced from 17 patients (8 with baseline only, 7 with progression only, and 2 with paired baseline and progression samples) across 7 trial sites. Trajectory inference analysis of tumor-infiltrating T cells revealed a bifurcating trajectory, starting with naïve T cells and ending either in PMCH+ terminally exhausted CD8+ T cells or SLAMF7+ CD8+ T cells. Notably, the SLAMF7+ T cell population expressed high levels of cytotoxic genes (including GZMA, GZMB, GNLY) and markers of tissue residency ( ZNF683/HOBIT and ITGAE/CD103), and had a restricted TCR diversity (normalized Shannon index = 0.57). Among patients with at least 100 sequenced T cells (n = 14), a higher percentage of SLAMF7+ CD8+ T cells (relative to total T cells) was associated with primary resistance (progressive disease [PD] as best response) to nivo (mean percentage in PD [n = 4] patients 32.7%; stable disease [n = 4] patients, 9.1%; complete or partial response [CR/PR; n = 6] patients, 2.2%; p = 0.019 for CR/PR vs PD). A signature derived using genes expressed in the T cell trajectory branch containing the SLAMF7+ CD8+ T cell population was used to interrogate bulk RNA-seq data from 172 pre-treatment tumors from the nivo arms of the CheckMate-009/010/025 trials. The signature score was enriched in patients with PD compared to CR/PR as best response (p = 0.032). Analysis of bulk whole exome sequencing and RNA-seq from patients enrolled in the HCRN GU16-260 is pending. Conclusions: Single-cell transcriptomic analysis uncovered a SLAMF7+ CD8 + T cell population with markers of cytotoxicity and tissue residency that was associated with resistance to nivo monotherapy in RCC. Further, the study highlights that scRNA-seq is a viable scientific strategy for deep correlative analysis in multicenter clinical trials.

Purpose: Patients discontinuing immuno-oncology regimens may experience periods of disease control without need for ongoing anticancer therapy, but toxicity may persist. We describe treatment-free survival (TFS), with and without toxicity. Patients and Methods: Data were analyzed from the randomized phase III CheckMate 214 trial of nivolumab plus ipilimumab (n = 550) versus sunitinib (n = 546) for treatment-naïve, advanced renal cell carcinoma (aRCC). TFS was estimated by the 42-month restricted mean times defined by the area between Kaplan–Meier curves for two time-to-event endpoints defined from randomization: time to protocol therapy cessation and time to subsequent systemic therapy initiation or death. TFS was subdivided as TFS with and without toxicity by counting days with ≥1 grade ≥3 treatment-related adverse event (TRAE). Results: At 42 months since randomization, 52% of nivolumab plus ipilimumab and 39% of sunitinib intermediate/poor-risk patients were alive; 18% and 5% surviving treatment-free, respectively. Among favorable-risk patients, 70% and 73% of nivolumab plus ipilimumab and sunitinib patients were alive; 20% and 9% treatment-free. Over the 42-month period, mean TFS was over twice as long after nivolumab plus ipilimumab than sunitinib for intermediate/poor-risk (6.9 vs. 3.1 months) and three times as long for favorable-risk patients (11.0 vs. 3.7 months). Mean TFS with grade ≥3 TRAEs was a small proportion of time for both treatments (0.6 vs. 0.3 months after nivolumab plus ipilimumab vs. sunitinib for intermediate/poor-risk, and 0.9 vs. 0.3 months for favorable-risk patients). Conclusions: Patients initiating first-line nivolumab plus ipilimumab for aRCC spent more survival time treatment-free without toxicity versus those on sunitinib, regardless of risk group.

T-cell receptor sequencing (TCRseq) enables tracking of T-cell clonotypes recognizing the same antigen over time and across biological compartments. TCRseq has been used to test if cross-reactive antitumor T cells are responsible for development of immune-related adverse events (irAEs) following immune checkpoint blockade. Prior studies have interpreted T-cell clones shared among the tumor and irAE as evidence supporting this, but interpretations of these findings are challenging, given the constraints of TCRseq. Here we capitalize on a rare opportunity to understand the impact of potential confounders, such as sample size, tissue compartment, and collection batch/timepoint, on the relative proportion of shared T-cell clones between an irAE and tumor specimens. TCRseq was performed on tumor-involved and -uninvolved tissues, including an irAE, that were obtained throughout disease progression and at the time of rapid autopsy from a patient with renal cell carcinoma treated with programmed death-1 (PD-1) blockade. Our analyses show significant effects of these confounders on our ability to understand T-cell receptor overlap, and we present mitigation strategies and study design recommendations to reduce these errors. Implementation of these strategies will enable more rigorous TCRseq-based studies of immune responses in human tissues, particularly as they relate to antitumor T-cell cross-reactivity in irAEs following checkpoint blockade.

Summary Background Cabozantinib is approved for patients with metastatic renal cell carcinoma on the basis of studies done in clear-cell histology. The activity of cabozantinib in patients with non-clear-cell renal cell carcinoma is poorly characterised. We sought to analyse the antitumour activity and toxicity of cabozantinib in advanced non-clear-cell renal cell carcinoma. Methods We did a multicentre, international, retrospective cohort study of patients with metastatic non-clear-cell renal cell carcinoma treated with oral cabozantinib during any treatment line at 22 centres: 21 in the USA and one in Belgium. Eligibility required patients with histologically confirmed non-clear-cell renal cell carcinoma who received cabozantinib for metastatic disease during any treatment line roughly between 2015 and 2018. Mixed tumours with a clear-cell histology component were excluded. No other restrictive inclusion criteria were applied. Data were obtained from retrospective chart review by investigators at each institution. Demographic, surgical, pathological, and systemic therapy data were captured with uniform database templates to ensure consistent data collection. The main objectives were to estimate the proportion of patients who achieved an objective response, time to treatment failure, and overall survival after treatment. Findings Of 112 identified patients with non-clear-cell renal cell carcinoma treated at the participating centres, 66 (59%) had papillary histology, 17 (15%) had Xp11.2 translocation histology, 15 (13%) had unclassified histology, ten (9%) had chromophobe histology, and four (4%) had collecting duct histology. The proportion of patients who achieved an objective response across all histologies was 30 (27%, 95% CI 19–36) of 112 patients. At a median follow-up of 11 months (IQR 6–18), median time to treatment failure was 6·7 months (95% CI 5·5–8·6), median progression-free survival was 7·0 months (5·7–9·0), and median overall survival was 12·0 months (9·2–17·0). The most common adverse events of any grade were fatigue (58 [52%]), and diarrhoea (38 [34%]). The most common grade 3 events were skin toxicity (rash and palmar-plantar erythrodysesthesia; five [4%]) and hypertension (four [4%]). No treatment-related deaths were observed. Across 54 patients with available next-generation sequencing data, the most frequently altered somatic genes were CDKN2A (12 [22%]) and MET (11 [20%]) with responses seen irrespective of mutational status. Interpretation While we await results from prospective studies, this real-world study provides evidence supporting the antitumour activity and safety of cabozantinib across non-clear-cell renal cell carcinomas. Continued support of international collaborations and prospective ongoing studies targeting non-clear-cell renal cell carcinoma subtypes and specific molecular alterations are warranted to improve outcomes across these rare diseases with few evidence-based treatment options. Funding None.

ICI therapy has shown unprecedented clinical outcomes in mRCC patients, but durable responses have been limited by innate (never respond initially) and acquired resistance (initially respond but eventually develop cancer progression). Establishment of predictive biomarkers for response to ICI maximizes the therapeutic benefit. Since no such marker exists, we investigated DC-HIL/GPNMB as a possibility because we detected DC-HIL to be elevated in blood of patients with metastasis, as both a receptor on myeloid-derived suppressor cells (MDSC) and as a soluble form (sDC-HIL); and found DC-HIL to be relevant to ICI resistance in mice. We studied 27 mRCC patients treated with combination ICI (Ab to PD1/PDL1/CTLA4) and assessed tumor response (by RECIST) at 12 wk after therapy. Blood was collected before and after treatment and assayed by FACS for expression of DC-HIL and PDL1 on CD14+HLA-DRno/lo monocytic (mMDSC) and CD15+CD11b+ granulocytic MDSC (gMDSC). T-cell suppressor function was assayed by cell culture. We showed both MDSC subsets to express DC-HIL predominantly over PDL1. We also showed mMDSC to be more potent T-cell suppressors than gMDSC (85% vs. 58% suppression, p=0.012) and to also be more dependent on DC-HIL for such suppression (56% vs. 15% restoration of T-cell function after adding DC-HIL mAb, p=0.013). However, there was no significant difference in % DC-HIL+MDSC/PBMC between ICI responders and non-responders (p=0.15). We next examined the relationship between tumor response (at 12 wk) and blood sDC-HIL (by ELISA) in 31 mRCC patients. At baseline, non-responders (n=10) had a significantly higher sDC-HIL than responders (n=21) (14 ± 2.4 vs. 10 ± 4.6 ng/ml, p=0.004), but no difference in blood PDL1 or VEGF. Among initial responders (n=22), 50% maintained a positive response while the other half acquired resistance after 20 wk. Among initial non-responders (n=9), 77% never responded while 22% responded positively after 20 wk. We then analyzed changes over time in sDC-HIL levels after treatment (up to 60 wks) in individuals. Patients who responded positively to ICI at treatment inception and through 40 wk maintained blood sDC-HIL at levels lower than the median for all positive responders. Initial responders who acquired resistance (9 out of 11 patients) had low blood sDC-HIL that rose during cancer progression. All constant non-responders (n=7) had high blood sDC-HIL that remained high during the study. To our surprise, the 2 initial non-responders who responded positively after 20-40 wk of ICI displayed an abrupt rise in blood sDC-HIL during their positive response. Our results indicate blood sDC-HIL as a promising biomarker for prognosticating response to ICI in mRCC patients. Citation Format: Jin-Sung Chung, Vijay Ramani, Ponciano D. Cruz, Hans J. Hammers, Kiyoshi Ariizumi. Elevated serum DC-HIL is associated with poor response to immune checkpoint inhibitors (ICI) in metastatic renal cell carcinoma (mRCC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1258.

TPS4605 Background: Tivozanib, a highly selective and potent vascular endothelial growth factor receptor tyrosine kinase inhibitor, has demonstrated single-agent efficacy in advanced renal cell carcinoma (aRCC) along with minimal off-target toxicities and a favorable adverse event (AE) profile (Rini et al Lancet Oncol 2020). Tivozanib was approved by the FDA on March 10, 2021, for the treatment of patients with aRCC who had progressed on 2 or more prior systemic therapies. Tivozanib was combined with Nivolumab in the phase 1b/2 TiNivo trial (NCT03136627), showing an objective response rate of 56%, disease control rate of 96%, median PFS of 18.9 months and a tolerable safety profile (Albiges et al Ann Oncol. 2021). Methods: TiNivo-2 (NCT04987203) is a phase 3, randomized, controlled, multicenter, open-label study to compare tivozanib in combination with nivolumab to tivozanib monotherapy in subjects with renal cell carcinoma who have progressed following 1-2 lines of therapy including an immune checkpoint inhibitor. Eligibility criteria include age >18 years, clear cell RCC, ECOG PS 0-1, and disease progression during or following at least 6 weeks of treatment with ICI for RCC. Subjects will be stratified by IMDC risk category and whether ICI was received in most recent line of treatment or not. Subjects will receive tivozanib 1.34 mg orally once daily for 21 consecutive days followed by 7 days off, on the monotherapy arm, and tivozanib 0.89 mg at the same schedule in addition to nivolumab 480mg intravenously every 4 weeks on the combination arm. Study assessments include CT scan or MRI of the chest, abdomen, and pelvis every 8 weeks following Cycle 1 Day 1 for 2 years and every 12 weeks thereafter until disease progression is confirmed by independent radiology review (IRR). The primary objective is to compare the progression-free survival (PFS) of tivozanib in combination with nivolumab to tivozanib. A sample size of 326 subjects, with 191 events will provide at least 80% power to detect a 50% improvement in PFS, 12 mos v. 8 mos, as assessed by an IRR. Secondary endpoints include assessment of overall survival (OS), objective response rate (ORR), and duration of response (DoR), as well as safety and tolerability. Exploratory endpoints are to assess the quality of life (FKSI-DRS and EORTC QLQ C-30) and to investigate the pharmacokinetics of tivozanib. TiNivo-2 is actively enrolling and planning to open at 190 sites in the United States, and the European Union. Clinical trial information: NCT04987203.

TPS4599 Background: In clear cell renal cell carcinoma (ccRCC) the constitutive expression of hypoxia induced factor 1-α leads to increased expression of AXL. AXL overexpression has been associated with the development of resistance to VEGF inhibitors and suppression of the innate immune response through inhibition of macrophage-driven inflammation. Batiraxcept is a recombinant fusion protein dimer containing an extracellular region of human AXL combined with the human immunoglobulin G1 heavy chain (Fc), which demonstrates highly potent, specific AXL inhibition. In preclinical studies using the 786-O, M62, and SN12L1 tumors, batiraxcept monotherapy resulted in a significant reduction of tumor growth compared to control. In healthy volunteer and ovarian cancer clinical studies, batiraxcept was well tolerated with no dose-related adverse events, and a maximum tolerated dose was not reached. Therefore, batiraxcept could be tested as either a monotherapy or in combination with standard of care drugs in patients with metastatic ccRCC. The Phase 1b dose-escalation portion of this study evaluated batiraxcept in combination with standard of care cabozantanib in patients who progressed on or after first line therapy. No DLT was observed at either of two batiraxcept doses evaluated. The recommended Phase 2 dose of batiraxcept has been identified as 15 mg/kg every 2 weeks (q2w) with cabozantinib 60 mg based upon safety, PK/PD, and preliminary efficacy data. Methods: This Phase 2, multi-center, open-label study includes three parts: Part A) batiraxcept 15 mg/kg q2w in combination with cabozantinib 60 mg daily for ccRCC subjects who have progressed on or after one line of therapy, n=25. Part B) batiraxcept 15 mg/kg q2w with cabozantinib 40 mg daily and nivolumab at the investigator’s choice (240 mg q2w or 480 mg q4w) for first line treatment of advanced or metastatic ccRCC subjects, n=20. If no safety signals are observed in the first 6 subjects enrolled, 10 subjects will be enrolled in the first stage of a Simon 2-stage minmax statistical design. If ≥ 6/10 subjects achieve PR or CR, stage 2 will open to enroll up to 20 total subjects. Part C) batiraxcept 15 mg/kg q2w monotherapy for subjects with advanced/metastatic ccRCC ineligible for curative intent therapies, n=10. The primary objective for each arm is objective response rate by RECIST v1.1. Secondary objectives include safety, duration of response, clinical benefit rate, progression free survival by RECIST v1.1, and overall survival. Exploratory objectives include pharmacokinetic and pharmacodynamic assessments. The Phase 2 portion of this Ph1b/2 study is currently enrolling. Clinical trial information: NCT04300140.

4511 Background: AXL is up-regulated by hypoxia-inducible factor-1 signaling in both VHL-deficient and hypoxic tumor cells and plays a critical role in the metastatic phenotype of ccRCC. Batiraxcept is a recombinant fusion protein containing an extracellular region of human AXL combined with the human immunoglobulin G1 heavy chain (Fc), demonstrating highly potent, specific AXL inhibition. Methods: Batiraxcept at doses of 15 and 20 mg/kg, plus cabozantinib 60 mg daily, was evaluated using a 3+3 dose escalation study design. The primary objective was safety; secondary and exploratory objectives included identification of the recommended phase 2 dose (RP2D), overall response rate (ORR), and duration of response (DOR). Correlation of serum soluble AXL (sAXL)/GAS6 with ORR was evaluated. Key eligibility criteria include previously treated (2L+) ccRCC patients; prior treatment with cabozantanib was not allowed. sAXL/GAS6 was evaluated at baseline. Results: Data as of 4-February-2022, Phase 1b enrolled 26 patients, 16 patients treated with 15 mg/kg and 10 patients with 20 mg/kg dose of batiraxcept. Baseline characteristics: median age 60 (40-81); male 22 (85%); median prior line of therapy 1 (1-5); IMDC risk group of favorable 6 (23%); prior VEGF inhibitor 15 (58%); 100% with prior immunotherapy. At median follow up of 4.9 months, 92% (n=24) patients remained on the study. No dose limiting toxicities were observed at either 15 mg/kg or 20 mg/kg dose. Batiraxcept and cabozantinib related adverse events (AEs) occurred in 17 subjects (65%). Most common related AE include decreased appetite 31% (n=8), diarrhea and fatigue 23% (n=6). Grade 3 related AEs occurred in 4 patients (15%) including diarrhea, thromboembolism, hypertension, small bowel obstruction, and thrombocytopenia (n=1, 4% each) being most common. No grade 4 or 5 related AEs were observed. The ORR was 46% (n=12, partial response [PR]; Table). No patients had primary progressive disease. Among the patients who had baseline sAXL/GAS6 ratio of ≥ 2.3, the ORR was 67% (12/18). Regardless of baseline sAXL/GAS6 ratio, 3-month DOR was 100%; and 6-month progression free survival was 79%. Batiraxcept PK levels were similar across both doses and GAS6 levels suppressed through the dosing period. Conclusions: Batiraxcept plus cabozantinib is well tolerated. The RP2D of batiraxcept was identified as 15 mg/kg. Early efficacy signals were observed including 100% DOR at 3 months. Baseline sAXL/GAS6 may serve as a potential biomarker to enrich the population. Clinical trial information: NCT04300140. [Table: see text]

4538 Background: The Lung Immune Prognostic Index (LIPI), defined by lactate dehydrogenase (LDH) and derived neutrophil to lymphocyte ratio (dNLR), has been shown to correlate with outcomes of immune checkpoint inhibitor therapy in patients (pts) with lung and other cancers, including pts with previously treated aRCC receiving nivolumab in the phase 2 NIVOREN GETUG-AFU 26 trial. We report an analysis of LIPI in pts with previously untreated aRCC receiving N+I or SUN in the randomized phase 3 CheckMate 214 trial with 5 years minimum follow-up. Methods: Data were used from CheckMate 214 comparing N+I (N 3 mg/kg + I 1 mg/kg) vs SUN (50 mg) for untreated aRCC (N = 1096). Pts with available LIPI data were categorized into 3 LIPI groups (good [LG], dNLR ≤ 3 and LDH ≤ upper limit of normal [ULN]); intermediate [LI], dNLR > 3 or LDH > ULN; and poor [LP], dNLR > 3 and LDH > ULN). This analysis focused on the prognostic value of LIPI using overall survival (OS) outcomes. Univariable analyses (UVAs) were conducted to evaluate LIPI groups alongside known risk factors including age, sex, IMDC risk, baseline PD-L1 status, prior nephrectomy, and baseline tumor burden. Variables that were statistically significant in UVAs ( P < 0.1) were included in the full multivariable analyses (MVAs), from which a reduced model was generated. Results: A total of 1085 pts were evaluable for LIPI (N+I, n = 542; SUN, n = 543). Pts were distributed evenly between treatment arms for all 3 LIPI groups, but distribution between LIPI groups was unbalanced, with most pts grouped as LG (Table). OS outcomes were improved with N+I over SUN across all LIPI groups. Moreover, pts in the LG group had better OS outcomes vs pts in the LI or LP groups regardless of treatment, but with more distinct differences between LIPI groups in the SUN arm (Table). Final MVA results showed the LIPI correlated with OS for LI vs LG in the N+I arm and for LI vs LG and LP vs LG in the SUN arm (Table). Conclusions: These results from CheckMate 214 indicate the potential prognostic value of the LIPI in pts with untreated aRCC receiving N+I or SUN. Additional analyses are ongoing to further investigate the prognostic value of LIPI in this pt population and its impact on other clinical outcomes. Clinical trial information: NCT02231749. [Table: see text]

2501 Background: The immunoregulatory cytokine IL-27 upregulates inhibitory immune checkpoint receptors (eg, PD-L1, TIGIT) and downregulates proinflammatory cytokines (eg, IFNγ, TNFα). SRF388 is a fully human IgG1 blocking antibody to IL-27 with potential to promote immune activation in the tumor microenvironment. A phase 1 study was conducted to establish the preliminary safety of SRF388 and to identify recommended phase 2 doses (RP2D) suitable for monotherapy and combination expansions (NCT04374877). Methods: The dose-escalation study (accelerated single patient followed by standard 3+3) enrolled patients (pts) with advanced treatment-refractory solid tumors. Upon RP2D selection, monotherapy and combination expansions opened for treatment-refractory clear cell renal cell cancer (ccRCC), hepatocellular cancer (HCC), and non-small cell lung cancer. SRF388 was administered IV every 4 weeks (wks) as monotherapy and every 3 wks with pembrolizumab. Tumor response was assessed by RECIST1.1. Results: The monotherapy dose-escalation enrolled 29 pts with doses ranging from 0.003 to 20 mg/kg. Median age was 64 years. Most pts were female (62%) with ECOG PS of 1 (72%). Approximately 80% had prior PD-(L)1 blockade, and 48% had ≥4 prior therapies. Treatment-related adverse events (TRAEs) occurred in 21%, and all were low grade. Fatigue was the only TRAE reported in ≥10% (n = 3). No dose-limiting toxicities (DLTs) or Grade ≥3 TRAEs were observed. Median time on study was 9 wks (range 0–59). One patient with highly treatment-refractory NSCLC experienced a confirmed partial response (PR) at 8 wks that was durable for 20 wks. Nine pts (31%) experienced disease stabilization at 8 wks, with 6 of 9 exhibiting durable disease control at 6 months. Of the 7 pts with ccRCC in the dose-escalation portion of the trial, 3 (43%) experienced durable disease control for ≥20 wks (range: 20-32). With doses up to 20 mg/kg, SRF388 PK remain linear with an estimated T1/2 of 10-12 days. PK characteristics and safety profile support dosing every 3 or 4 wks. Based on safety, tolerability, PK, peripheral pSTAT1 inhibition, and preliminary efficacy, 10 mg/kg was selected as the RP2D. Both the pembrolizumab safety cohort (n = 10) and Stage 1 of the ccRCC monotherapy expansion (n = 17) have fully enrolled. Of the 10 evaluable pts with ccRCC, 1 confirmed monotherapy PR has been reported, enabling Stage 2 initiation. Changes in several serum cytokines and chemokines were observed after SRF388 administration, including expected increase in circulating IL-27 levels. Conclusions: Results of IL-27 pathway blockade with a first-in-class therapeutic demonstrates that SRF388 has good tolerability with encouraging preliminary antitumor activity as a monotherapy. Updated data, including safety and clinical outcomes as well as correlative biomarker analyses, will be presented. Clinical trial information: NCT04374877.

Background The optimal timing of targeted therapy (TT) initiation for metastatic renal-cell carcinoma (mRCC) is not clear. We used a nationwide cancer registry to determine clinical and social factors associated with delayed TT and to evaluate the association of a delayed approach with overall survival (OS). Patients and Methods We performed a retrospective observational study utilizing the National Cancer Data Base from 2006 to 2012 for patients diagnosed with mRCC (clear-cell histology) treated with cytoreductive nephrectomy and TT. Time to initiation of TT was defined as early (within 2 months), moderately delayed (2-4 months), delayed (4-6 months), and late (> 6 months). Results Of the 2716 patients included in the analysis, the median (interquartile range) time from diagnosis to initiation of TT was 2.1 (1.3-3.23) months. A total of 1255 patients (46.2%) had early TT, 1072 patients (39.5%) had moderately delayed TT, 284 patients (10.5%) had delayed TT, and 105 patients (3.9%) had late TT. Delay in TT initiation was not independently associated with OS in multivariable analysis. The time interval from diagnosis to TT initiation was not correlated with time from initiation of TT to death (r = 0.04, P = .08). Conclusion We found that delayed initiation of TT was not an independent predictor of worse OS. Although this study is subject to limitations of observation study design and selection bias, the results are consistent with the notion that in carefully selected patients, outcomes might not be compromised with initial observation.

INTRODUCTION: Immune checkpoint inhibitors (ICIs) have become a standard of care in metastatic renal cell carcinoma (mRCC) but are associated with immune-related adverse events (irAEs) including colitis. Growing evidence suggests proton pump inhibitors (PPIs) increase the risk of inflammatory bowel disease (IBD). Given the pathophysiological overlap between IBD and ICI colitis, we sought to evaluate the relationship between PPI use and ICI colitis in mRCC patients. PATIENTS AND METHODS: We performed a retrospective study of adult patients who received ICI therapy for mRCC between 2015 and 2018 at University of Texas Southwestern Medical Center affiliated hospitals. Clinical characteristics, oncological outcomes, ICI colitis details, and PPI use details were collected by manual chart review. The diagnosis of ICI colitis was made via biopsy when available, or by clinical criteria (symptoms and response to immunosuppressive therapy) when biopsy specimens were unavailable or inconclusive. Univariable and multivariable logistic regression analyses were conducted to assess the potential contribution of PPIs to ICI colitis. RESULTS: A total of 176 patients received ICI therapy for mRCC, of which 16 (9.1%) were diagnosed with ICI colitis. Patients with ICI colitis presented with elevated stool lactoferritin and calprotectin and a wide range of endoscopic and histologic findings. There were no significant differences between patients with and without ICI colitis in age, gender, medical comorbidities, RCC history, and overall survival. However, exposure to ipilimumab and PPI use were more frequently observed in patients with ICI colitis than those without. In univariable and multivariable logistic regression analyses, exposure to ipilimumab and chronic use of PPIs >8 weeks were significantly associated with ICI colitis. CONCLUSION: In addition to ipilimumab use, chronic use of PPIs may be associated with ICI colitis in patients with mRCC.

313 Background: First-line NIVO+IPI demonstrates superior survival and response benefits in intent-to-treat (ITT) patients (pts) with aRCC after long-term follow-up in the phase 3 CheckMate 214 trial. Data are scarce on tumor relapse and patterns of disease progression with immuno-oncology agents in this setting. This exploratory analysis of CheckMate 214 characterizes patterns of progression with NIVO+IPI vs SUN with 4 years minimum follow-up. Methods: Pts with clear cell aRCC were randomized to NIVO+IPI Q3W×4 followed by NIVO monotherapy Q2W, or SUN QD×4 weeks (6-week cycle). Patterns of progression were characterized in ITT pts and analyzed post hoc using descriptive statistics. Progression patterns were defined by ≥ 20% target lesion growth (T), unequivocal progression of nontarget lesions (NT), and new lesion(s) (NL). Response and progression were assessed per independent radiology review committee via RECIST v1.1. Results: Radiographic progression (RP) was documented in 299/550 (54.4%) ITT pts with NIVO+IPI vs 289/546 (52.9%) with SUN. Among ITT pts with a confirmed response (objective response = 215/550 [39.1%, NIVO+IPI] vs 177/546 [32.4%, SUN]), 71/215 (33.0%) vs 84/177 (47.5%) pts experienced post-response RP with NIVO+IPI vs SUN; 8/59 (13.6%) vs 3/14 (21.4%) progressed after complete response, and 63/156 (40.4%) vs 81/163 (49.7%) progressed after partial response, respectively. The pattern of RP differed between arms (Table). With NIVO+IPI, 106/299 (35.5%) RPs resulted from NL only vs 74/289 (25.6%) with SUN, and this differential was more pronounced in pts with an initial confirmed response (36/71 [50.7%] vs 23/84 [27.4%]). Most NL-only RPs in initial responders occurred in a single organ (34/36 [94.4%] for NIVO+IPI; 20/23 [87.0%] for SUN) with the most common being lymph nodes (11/34 [32.4%]), brain (8/34 [23.5%]), and lung (5/34 [14.7%]) with NIVO+IPI, and lymph nodes (7/20 [35.0%]), brain (4/20 [20.0%]) and adrenal gland (3/20 [15.0%]) with SUN. Additional progression details, baseline characteristics, and key efficacy outcomes in progressors will be reported. Conclusions: Differential patterns of tumor relapse and disease progression were observed after long-term follow up of patients treated with NIVO+IPI vs SUN in CheckMate 214. NL-only progression occurred more often with NIVO+IPI vs SUN, in particular in the subset of pts who progressed post-response. These patterns may have therapeutic implications. Clinical trial information: NCT02231749 . [Table: see text]

Introduction : The Metastatic Renal Cell Carcinoma (MaRCC) Registry provides prospective data on real-world treatment patterns and outcomes in patients with metastatic renal cell carcinoma (mRCC). Methods and Materials : Patients with mRCC and no prior systemic therapy were enrolled at academic and community sites. End of study data collection was in March 2019. Outcomes included overall survival (OS). A survey of treating physicians assessed reasons for treatment initiations and discontinuations. Results : Overall, 376 patients with mRCC initiated first-line therapy; 171 (45.5%) received pazopanib, 75 (19.9%) sunitinib, and 74 (19.7%) participated in a clinical trial. Median (95% confidence interval) OS was longest in the clinical trial group (50.3 [35.8–not reached] months) versus pazopanib (39.0 [29.7–50.9] months) and sunitinib 26.2 [19.9–61.5] months). Non-clear cell RCC (21.5% of patients) was associated with worse median OS than clear cell RCC (18.0 vs 47.3 months). Differences in baseline characteristics, treatment starting dose, and relative dose exposure among treatment groups suggest selection bias. Survey results revealed a de-emphasis on quality of life, toxicity, and patient preference compared with efficacy in treatment selection. Conclusion : The MaRCC Registry gives insights into real-world first-line treatment selection, outcomes, and physician rationale regarding initial treatment selection prior to the immunotherapy era. Differences in outcomes between clinical trial and off-study patients reflect the difficulty in translating trial results to real-world patients, and emphasize the need to broaden clinical trial eligibility. Physician emphasis on efficacy over quality of life and toxicity suggests more data and education are needed regarding these endpoints. MicroAbstract : The Metastatic Renal Cell Carcinoma Registry provides prospective data on real-world treatment patterns and outcomes in patients with metastatic renal cell carcinoma (mRCC). 376 patients with mRCC and no prior systemic therapy were included in this study. This report describes initial real-world treatment patterns. Physician emphasis on efficacy over quality of life and toxicity suggests more data and education are needed.

Immune checkpoint inhibitors (ICI) have revolutionized the field of oncology. Although rare (

The incidence of renal cell carcinoma (RCC) has been increasing, with a moderate subgroup of individuals who later develop metastatic disease. Historically, metastatic RCC has been managed with systemic therapy because RCC was believed to be radioresistant. Local therapies, such as stereotactic body radiation therapy, also known as stereotactic ablative radiotherapy, which utilize focused high-dose-rate radiation delivered over a limited number of treatments, have been successful in controlling local disease and, in some cases, extending survival in patients with intracranial and extracranial metastatic RCC. Stereotactic ablative radiotherapy is highly effective in treating intact disease when patients are not surgical candidates. Stereotactic ablative radiotherapy is well tolerated when used in conjunction with systemic therapy such as tyrosine kinase inhibitors and immune checkpoint inhibitors. These successes have prompted investigators to evaluate the efficacy of stereotactic body radiation therapy in novel settings such as neoadjuvant treatment of advanced RCC with tumor thrombus and oligometastatic/oligoprogressive disease states.

Immune checkpoint inhibitors (ICIs) such as nivolumab and ipilimumab have improved outcomes in metastatic renal cell carcinoma (mRCC) patients, but they are also associated with immune-related adverse events (irAEs). As observed in melanoma, we hypothesized that patients experiencing an autoimmune reaction directed against the tissue of origin may be more likely to benefit from ICI. Specifically, we asked whether patients with immune-related acute interstitial nephritis (irAIN) exhibited improved outcomes. Using Kidney Cancer Explorer (KCE), a data portal and i2b2-based central database for clinical, pathological and experimental genetic data, we systematically identified all patients with mRCC at UT Southwestern Medical Center (UTSW) from 2014–2018 who received at least one dose of ICI. More recent cases were identified through a provider query. We extracted creatinine (Cr) values at baseline and over the entirety of each patient ICI treatment course using KCE. Patients with ≥ 1.5-fold Cr increase over baseline were investigated. The likelihood of irAIN was determined based on the work-up (biopsy, if available), or by clinical criteria (timing of kidney injury, exclusion of other etiologies, treatment with immunosuppressants and response). We identified 177 mRCC patients who received at least one dose of ICI, 36 of whom had ≥ 1.5-fold increase in Cr over baseline while on treatment. Of those, two had biopsy-proven irAIN and one was clinically diagnosed, resulting in an incidence of 1.7%. One additional biopsy-proven case past 2018 was identified through a provider query, for a total of four patients. Two received combination nivolumab and ipilimumab in the first line, whereas the remaining received nivolumab after first line therapy. irAIN onset ranged from 1.5 to 12 months. All four patients stopped ICI with recovery of renal function, at least partially, three after receiving systemic steroids. Notably, all four patients had a deep response. In conclusion, irAIN is a rare event, but it may portend a higher likelihood of response. One possible explanation is antigenic overlap between normal renal tubular cells and tumor cells.

BackgroundThe extent to which response and survival benefits with immunotherapy-based regimens persist informs optimal first-line treatment options. We provide long-term follow-up in patients with advanced renal cell carcinoma (aRCC) receiving first-line nivolumab plus ipilimumab (NIVO+IPI) versus sunitinib (SUN) in the phase 3 CheckMate 214 trial. Survival, response, and safety outcomes with NIVO+IPI versus SUN were assessed after a minimum of 42 months of follow-up.MethodsPatients with aRCC were enrolled from October 16, 2014, through February 23, 2016. Patients stratified by International Metastatic Renal Cell Carcinoma Database Consortium (IMDC) risk and region were randomized to nivolumab (3 mg/kg) plus ipilimumab (1 mg/kg) every 3 weeks for four doses, followed by nivolumab (3 mg/kg) every 2 weeks; or SUN (50 mg) once per day for 4 weeks (6-week cycle). Primary endpoints: overall survival (OS), progression-free survival (PFS), and objective response rate (ORR) per independent radiology review committee in IMDC intermediate-risk/poor-risk patients. Secondary endpoints: OS, PFS, and ORR in the intention-to-treat (ITT) population and safety. Favorable-risk patient outcomes were exploratory.ResultsAmong ITT patients, 550 were randomized to NIVO+IPI (425 intermediate/poor risk; 125 favorable risk) and 546 to SUN (422 intermediate/poor risk; 124 favorable risk). Among intermediate-risk/poor-risk patients, OS (HR, 0.66; 95% CI, 0.55–0.80) and PFS (HR, 0.75; 95% CI, 0.62–0.90) benefits were observed, and ORR was higher (42.1% vs 26.3%) with NIVO+IPI versus SUN. In ITT patients, both OS benefits (HR, 0.72; 95% CI, 0.61–0.86) and higher ORR (39.1% vs 32.6%) were observed with NIVO+IPI versus SUN. In favorable-risk patients, HR for death was 1.19 (95% CI, 0.77–1.85) and ORR was 28.8% with NIVO+IPI versus 54.0% with SUN. Duration of response was longer (HR, 0.46–0.54), and more patients achieved complete response (10.1%–12.8% vs 1.4%–5.6%) with NIVO+IPI versus SUN regardless of risk group. The incidence of treatment-related adverse events was consistent with previous reports.ConclusionsNIVO+IPI led to improved efficacy outcomes versus SUN in both intermediate-risk/poor-risk and ITT patients that were maintained through 42 months’ minimum follow-up. A complete response rate >10% was achieved with NIVO+IPI regardless of risk category, with no new safety signals detected in either arm. These results support NIVO+IPI as a first-line treatment option with the potential for durable response.Trial registration numberNCT02231749.

The optimal management approach to advanced or metastatic renal cell cancer of the clear cell type continues to rapidly evolve. Risk stratification of patients into favorable-, intermediate-, and poor-risk categories is now routinely performed. In selected individuals with low-volume indolent disease, active surveillance may be an appropriate option. Cytoreductive nephrectomy and/or surgical metastasectomy may be also be considered for selected patients after evaluation by a multidisciplinary tumor board. Systemic frontline therapy options now include immune checkpoint inhibitor–based combination (IBC) therapies such as pembrolizumab/axitinib, nivolumab/ipilimumab, and avelumab/axitinib. With unusual exceptions, monotherapy with vascular growth factor receptor tyrosine kinase inhibitors or mTOR inhibitors are no longer appropriate options in the frontline setting. Despite the established efficacy of frontline IBC, most patients will ultimately require additional lines of therapy, and oncologists must think carefully when switching to another therapy, particularly in situations of drug intolerance or apparent disease progression. Systemic therapy options after IBC are generally tyrosine kinase inhibitor–based, and ongoing clinical trials will help optimize the treatment algorithm further. Despite many recent drug approvals for renal cell cancer (RCC), there remains a pressing need to identify new therapeutic targets. Finally, other systemic therapy or supportive care approaches must be considered for special patient populations such as those with poor performance status, end-organ dysfunction, brain metastases, or who have undergone metastasectomy.

INTRODUCTION AND OBJECTIVE:Immune checkpoint inhibitors (ICI) were approved for treating metastatic renal cell carcinoma (mRCC) in 2015. Current use of cytoreductive nephrectomy (CN) is guided by e...

288 Background: Nivolumab (nivo) is FDA approved for patients (pts) with VEGFR TKI-resistant RCC and the nivo + ipilimumab (nivo/ipi) combination is FDA approved for treatment naïve pts with IMDC intermediate and poor risk renal cell carcinoma (RCC). Little information was available on the efficacy and toxicity of nivo monotherapy in treatment naïve RCC or the efficacy of nivo/ipi salvage in pts with tumors resistant to initial nivo monotherapy. Methods: Eligible pts with treatment naïve RCC received nivo 240mg IV q2 wk x 6 doses followed by 360mg IV q3 wk x 4 doses followed by 480 mg q4 wk until progressive disease (PD), toxicity, or completion of 96 wks of treatment (Part A). Pts with PD prior to, or stable disease (SD) at 48 wks (pSD) were potentially eligible to receive salvage nivo (3mg/kg)/ipi (1 mg/kg) q3 wk x 4 doses followed by q4 wk nivo maintenance for up to 48 wks (Part B). All pts were required to submit tissue from a metastatic lesion obtained within 12 months (mos) prior to study entry and prior to Part B for correlative studies. Results: 123 pts with clear cell(cc) RCC were enrolled between 5/2017 and 12/2019 at 12 participating HCRN sites. Data lock was 04/07/2021. Median Follow-up 26.9 mos. Median age 65 (32-86) years; 72% male. IMDC risk: favorable (Fav) 35 (28%), intermediate (I) 76 (62%) and poor (P) 12 (10%). 22 (18%) had a component of sarcomatoid histology (SARC). RECIST defined ORR was: 34.1% (25.8-43.2%) (CR 6.5%, PR 27.6%), SD 47 (35.8%). ORR by irRECIST was 39%. ORR by IMDC was: Fav 20/35 (57.1%) (39-74%), (I/P) 22/88 (25%) and for SARC 36.4%. ORR by PD-L1 status was 21/78 (27%), 8/16 (50%) and 6/8 (75%) for pts with tumor PD-L1 of 0, 1-20 or > 20%, respectively (trend test p-value 0.002). 5/7 (71.4%) Fav pts with PD-L1 > 1 responded. Median DOR was 27.6 (13.7, NA) mos with 26/42 responders including 17/20 (85%) with Fav Risk remaining progression free. Median PFS was 8.2 (5.5, 10.9) mos; (30.3 for IMDC Fav and 5.4 for I/P). 91 pts remain alive with 24 mos OS rate of 78%. 65 patients (59 PD, 6 pSD) were potentially eligible for salvage nivo/ipi (Part B), but 25 did not enroll due to symptomatic PD (6), grade 3-4 toxicity on nivo (17), or other (2) and 5 were not treated due to inability to confirm residual disease on a biopsy. ORR for Part B by RECIST was 11.4% (4/35) and by irRECIST 17.2%. Grade 3-5 treatment-related AEs (TrAE) (not including asymptomatic amylase/lipase) were seen in 20.3% in Part A and 14.2% in Part B with 1 death in each cohort. Conclusions: Nivo monotherapy is active in treatment naïve ccRCC across all IMDC groups. Although efficacy appears less than combination nivo/ipi in I/P pts, Fav pts had a notably high ORR and DOR. Efficacy appeared to correlate with tumor PD-L1 status, although at least half the responders had a tumor PD-L1 of 0. Salvage treatment with nivo/ipi after nivo was frequently not feasible and of limited benefit. Clinical trial information: NCT03117309.

287 Background: RCC has a distinct pattern of metastatic spread with common sites of metastasis including the lung, bone, and liver. Less common sites include the brain, adrenal gland, and pancreas. While the pattern of metastatic spread has prognostic significance, the biology driving tropism to specific organ sites has not been fully characterized. We utilized a multi-institutional real-world dataset to examine genomic alterations and transcriptional signatures across the spectrum of metastatic sites in patients with RCC. Methods: RCC tissue specimens derived from the kidney and distant metastatic sites were sequenced utilizing a commercially available Clinical Laboratory Improvement Amendments (CLIA)-certified assay by Caris Life Sciences. Whole exome and transcriptome sequencing was performed. Molecular subgroups were defined according to the IMmotion151 metastatic RCC subtypes, with subgroups determined by a weighted average of gene expression levels. Molecular analysis and PD-L1 expression (SP142) were described by metastasis site. Results: 657 RCC samples from 653 patients underwent molecular profiling. The median age was 62 years (range 14-90) and the majority were male (70.6%). The most common histology was clear cell RCC (n = 509, 77.5%), followed by papillary (n = 63, 9.6%), chromophobe (n = 30, 4.6%), medullary (n = 8, 1.2%), collecting duct (n = 6, 0.9%), and mixed (n = 41, 6.2%). Specimen source included the kidney (n = 340, 51.8%), lung (n = 75, 11.4%), bone (n = 45, 6.8%), lymph nodes (n = 34, 5.2%), liver (n = 28, 4.3%), endocrine glands (adrenal, pancreas, and thyroid; n = 23, 3.5%), brain/CNS (n = 16, 2.4%), and other metastatic sites (n = 96, 14.6%). Compared to kidney, several genes were mutated at higher rates for select metastatic sites, including PBRM1 (59.5% bone, 59.1% endocrine, and 45.9% lung vs 33.8% kidney, p< 0.05) and KDM5C (27.8% endocrine, 29.2% lymph nodes, and 35.3% soft tissue vs 9.3% kidney, p< 0.05). When evaluating metastatic specimens versus kidney specimens, bone metastases had a significantly higher proportion of tumors classified as ‘Angio/stromal’ (n = 19, 42.2%; vs n = 52, 15.4%; p< 0.0001), while liver metastases had a higher proportion of the ‘complement/Ω-oxidation’ subgroup (n = 17, 60.7%; vs n = 48, 14.1%; p< 0.0001). PD-L1 expression in metastatic sites (range 6.8%-21.7%, with exception of 0% in GI; p= 0.09 to 0.99) was not significantly different from the kidney (16.6%). Conclusions: In our contemporary real-world analysis, we demonstrate differential patterns of molecular alterations among sites of metastasis in RCC. Our observations elucidate the biology underlying heterogeneous disease outcomes associated with site of metastasis. Application of predictive signatures by site of metastasis may help inform personalized therapy strategies in advanced RCC. Further studies are warranted to validate our findings.

389 Background: Emerging data suggest that active surveillance (AS) may be safely implemented in a subset of patients (pts) with metastatic renal cell carcinoma (RCC) and indolent disease to delay the initiation of systemic therapy without undermining long-term survival. However, widespread adoption of AS has been limited by a lack of data on factors portending favorable outcomes. In this study we sought to characterize pts undergoing AS at a large academic medical center to identify factors associated with time on AS. Methods: We identified pts on AS using Kidney Cancer Explorer (KCE), the data management platform of the Kidney Cancer Program at UT Southwestern Medical Center (2005-2020), as well as input from medical oncologists. The AS cohort was defined by (1) having metastatic RCC (determined by either a suspicious lesion > 1cm or a positive biopsy), and (2) the absence of prior systemic therapy. Baseline characteristics and IMDC criteria were evaluated at the outset. Outcomes of interest included progression free survival (PFS), time to systemic therapy (TST), and overall survival (OS). Survival estimates were generated using Kaplan Meier methods. Cox proportional hazard models were used in univariate and multivariate analyses to identify baseline characteristics associated with TST. Results: We identified 37 pts with metastatic RCC undergoing AS; 31 pts (83.8%) had ccRCC, 28 pts (75.7%) had a favorable IMDC prognostic group, 18 pts (48.6%) had one metastatic lesion at baseline, and the cohort had an average tumor burden of 21mm. The majority of pts had clinical or radiologic progression with a median PFS of 10.8 months (95% CI: 8.13-23.31). The median TST was 37 months (95% CI: 24.3-94.9). In total, there were 11 deaths (none of which occurred prior to the initiation of systemic therapy) and median OS after the initiation of AS was 132.5 months (95% CI: 87.3-NR). Multivariate analyses showed that higher numbers of metastatic lesions at baseline were associated with a shorter TST (HR:1.45; 95% CI: 1.03-2.03, p = 0.03). At a median follow-up of 62.5 months, 11/37 (29%) of pts had not yet started systemic therapy. Conclusions: These results expand upon previous studies and support a role for AS to delay systemic therapy in selected pts with metastatic RCC.

Background Combination treatment with immune checkpoint inhibitors and antiangiogenic drugs has shown encouraging preliminary antitumor activity across various tumor types including advanced or metastatic renal cell carcinoma (aRCC). The open-label, parallel-cohort, dose-escalation, phase I CheckMate 016 study evaluated the efficacy and safety of nivolumab in combination with antiangiogenic tyrosine kinase inhibitors or ipilimumab. Long-term outcomes from this study for the combination of nivolumab plus sunitinib or pazopanib in aRCC are presented. Methods Patients with aRCC received nivolumab plus either sunitinib (50 mg/day, 4 weeks on/2 weeks off; N + S) or pazopanib (800 mg/day; N + P) until progression/unacceptable toxicity. The nivolumab starting dose was 2 mg/kg every 3 weeks, with planned escalation to 5 mg/kg every 3 weeks. Primary endpoints were safety and tolerability; antitumor activity was a secondary endpoint. Results Arm N + S enrolled 33 patients, 19 of whom were treatment-naïve; this arm advanced to the expansion phase. Median follow-up was 50.0 months. Patients experienced high frequencies of adverse events (AEs) including treatment-related AEs (100%), grade 3/4 treatment-related AEs (82%), and treatment-related AEs leading to discontinuation (39%). Investigator-assessed objective response rate (ORR) was 55% (18/33) and median progression-free survival (PFS) was 12.7 months. Median overall survival (OS) was not reached. Arm N + P enrolled 20 patients, all had ≥1 prior systemic therapy; this arm was closed due to dose-limiting toxicities and did not proceed to expansion. Median follow-up was 27.1 months. Patients treated with N + P experienced high frequencies of AEs including treatment-related AEs (100%), grade 3/4 treatment-related AEs (70%), and treatment-related AEs leading to discontinuation (25%). Investigator-assessed ORR was 45% (9/20) and median PFS was 7.2 months. Median OS was 27.9 months. Conclusions The addition of standard doses of sunitinib or pazopanib to nivolumab resulted in a high incidence of high-grade toxicities limiting future development of either combination regimen. While there was no adverse impact on response and the OS outcome was notable, the findings suggest that the success of combination regimens based on immune checkpoint inhibitors and antiangiogenic drugs may be dependent on careful selection of the antiangiogenic component and dose. Trial registration Clinicaltrials.gov identifier: NCT01472081. Registered 16 November 2011. Electronic supplementary material The online version of this article (10.1186/s40425-018-0420-0) contains supplementary material, which is available to authorized users.

The approval of immunotherapeutic agents and immunotherapy-based combination strategies in recent years has revolutionized the treatment of patients with advanced renal cell carcinoma (aRCC). Nivolumab, a programmed death 1 (PD-1) immune checkpoint inhibitor monoclonal antibody, was approved as monotherapy in 2015 for aRCC after treatment with a VEGF-targeting agent. In April 2018, the combination of nivolumab and ipilimumab, a CTLA-4 inhibitor, was approved for intermediate- and poor-risk, previously untreated patients with aRCC. Then, in 2019, combinations therapies consisting of pembrolizumab (anti-PD-1) or avelumab (anti-PD-ligand (L) 1) with axitinib (a VEGF receptor tyrosine kinase inhibitor) were also approved to treat aRCC and are likely to produce dramatic shifts in the therapeutic landscape. To address the rapid advances in immunotherapy options for patients with aRCC, the Society for Immunotherapy of Cancer (SITC) reconvened its Cancer Immunotherapy Guidelines (CIG) Renal Cell Carcinoma Subcommittee and tasked it with generating updated consensus recommendations for the treatment of patients with this disease.

BackgroundIn clear cell renal cell carcinoma (ccRCC) the constitutive expression of hypoxia induced factor 1-α leads to increased expression of AXL. AXL overexpression has been associated with the development of resistance to VEGF inhibitors and suppression of the innate immune response through inhibition of macrophage-driven inflammation. AVB-S6-500 (AVB-500) is recombinant fusion protein dimer containing an extracellular region of human AXL combined with the human immunoglobulin G1 heavy chain (Fc), which demonstrates highly potent, specific AXL inhibition. In mouse ccRCC xenograft models, AVB-500 showed significantly more tumor reduction in combination with pazopanib versus pazopanib alone. In a Ph1b study of AVB-500 plus chemotherapy in platinum-resistant ovarian cancer (NCT03639246), no dose limiting toxicity (DLT) or treatment discontinuation due to adverse events was observed. The recommended phase 2 dose (RP2D) of 15 mg/kg was established by a model-informed drug development (MIDD) approach.MethodsThe P1b portion of this trial is a 3+3 dose escalation study to evaluate safety, pharmacokinetics, and pharmacodynamics of AVB 500 in combination with cabozantinib 60 mg daily. Dose levels of AVB-500 may include 15, 20, and 25 mg/kg every two weeks. The primary objective is to evaluate safety and tolerability. Secondary objectives include identification of the RP2D of AVB-500 and clinical activity. Key eligibility criteria include clear cell histology RCC and at least one prior line of therapy administered in the advanced or metastatic setting.ResultsAs of July 21, 2021, seven patients have received at least one dose of AVB-500 15 mg/kg and cabozantinib, with six patients ongoing treatment. No DLTs were observed. Trough levels at C1D15 were above the minimally efficacious concentration (MEC) identified from MIDD and GAS6 (AXL ligand) levels were suppressed prior to C2D1. Partial responses were observed in 3 of 5 patients (table 1); all patients demonstrated tumor decrease from baseline.Abstract 424 Table 1Preliminary clinical activity in NCT04300140ConclusionsAVB-500 in combination with cabozantanib demonstrates promising preliminary clinical activity and tolerability in patients with ccRCC. AVB-500 15 mg/kg is the presumptive RP2D with C1D15 AVB-500 troughs consistently above MECs observed. Safety, PK/PD and clinical activity will be updated at the time of presentation. (NCT04300140)Ethics ApprovalThis study has obtained ethics approval from WIRB Institutional Review Board®, Protocol ID #20200159, and all subjects provided informed consent prior to taking part in this study.

Purpose Oligoprogression, defined as limited sites of progression on systemic therapy, in patients with metastatic renal cell carcinoma (mRCC) is not uncommon, possibly because of inter- and intratumoral heterogeneity. We evaluated the effect of stereotactic ablative radiation therapy (SAbR) for longitudinal control of oligoprogressive mRCC. Methods and Materials Patients with extracranial mRCC were included in this retrospective analysis if they progressed in ≤3 sites on systemic therapy while demonstrating response/stability at other sites and received SAbR to all progressing sites without switching systemic therapy. Our primary endpoint was modified progression-free survival (mPFS), which we calculated from the start of SAbR to the start of a subsequent systemic therapy, death, or loss to follow-up. Results We identified 36 patients with a median follow-up of 20.4 months (interquartile range, 10.9-29.4). Forty-three sites were treated with SAbR with a median dose of 36 Gy (range, 18-50) in 3 fractions (range, 1-5). Median time to SAbR from the start of systemic therapy was 11.4 months (interquartile range, 6.1-17.1). Median mPFS was 9.2 months (95% confidence interval [CI], 5.9-13.2). Patients receiving SAbR while on immunotherapy exhibited a longer median mPFS (>28.4 months, log-rank P = .0001) than patients not on immunotherapy (9.2 months). Median overall survival from SAbR administration was 43.4 months (95% CI, 21.5-not Reached). The 1-year local control rate was 93% (95% CI, 78.7-97.5). Most SAbR-related toxicities were grade 1 to 2 (33% of patients), with one grade 5 hemoptysis event possibly related to SAbR or disease progression. Conclusions SAbR has the potential to extend the the duration of current systemic therapy for selected patients with mRCC, preserving subsequent therapies for later administration possibly enabling longer treatment duration.