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631 Background: Combination therapy with A + Ax in patients with previously untreated aRCC has shown superior progression-free survival (PFS) and objective response rate (ORR) vs sunitinib across all International Metastatic RCC Database Consortium (IMDC) risk groups. This study reports 24-month real-world outcomes in patients with aRCC receiving A + Ax in the UK. Methods: Patients were recruited from 9 UK sites. Inclusion criteria were diagnosis of aRCC, initiation of A + Ax on or after August 1, 2019, via the Early Access to Medicines Scheme, and age ≥18 years. The primary endpoints were overall survival (OS), PFS, ORR, and best response at 24 months post-A + Ax initiation. Data were analyzed descriptively. Total recruitment was 130 patients. Follow-up will continue until July 2023. Results: This analysis includes 78 patients with a minimum follow-up of 24 months. Median age at baseline was 66.6 years (range, 39.8-84.1 years); 76% (n=59) of patients were male, 63% (n=49) were White, 5% (n=4) were Asian/Asian British, and ethnicity was not recorded in 32% (n=25); 91% (n=71) had an Eastern Cooperative Oncology Group score of 0 or 1. IMDC risk status was favorable in 42% (n=33) of patients, intermediate in 41% (n=32), and poor in 17% (n=13). Median time between aRCC diagnosis and A + Ax initiation was 2.5 months (range, 0.03-90.4 months; n=77). Clear cell histology was the most prevalent (81% [n=63]); 68% (n=53) of patients had undergone nephrectomy, and 74% (n=58) had 1 or 2 metastatic sites at the index date. The OS rate at 24 months was 60% (95% CI, 49.4%-71.1%). The OS rates by IMDC risk status were: favorable, 76% (95% CI, 61.1%-90.4%); intermediate, 63% (95% CI, 45.7%-79.3%); and poor, 15% (95% CI, 0%-35.0%). The PFS rate at 24 months was 31% (95% CI, 20.5%-41.0%); median PFS was 9.1 months (95% CI, 7.9-13.4 months). ORR (n=76) at 24 months was 59% (95% CI, 48.2%-70.3%), with 4% (n=3) achieving complete response (CR) and 55% (n=42) partial response (PR). Best responses observed within 24 months were CR in 4% (n=3), PR in 54% (n=42), stable disease in 29% (n=23), and progressive disease in 10% (n=8) (2 not recorded). Median duration of response was 11.9 months (range, 0.4-23.7 months). Median time to discontinuation (TTD) of either A or Ax was 5.5 months (range, 0.5-20.5 months; n=50). Median TTD of A + Ax combined was 5.6 months (range, 0.8-20.5 months; n=43). Of 78 patients, 62 experienced an adverse event (AE) due to A + Ax treatment, 8 of whom had 14 serious AEs in total. The most common AEs were diarrhea (n=31), fatigue (n=22), and rash or oral mucositis (n=18 each); 3 patients discontinued Ax due to AEs including diarrhea (n=2), abnormal hepatic function (n=1), and abdominal pain (n=1). Conclusions: This UK-based real-world study of A + Ax treatment reports 24-month clinical outcomes in patients with aRCC. OS, PFS, ORR, and best response were in line with findings from prior clinical trials, with no new emerging AEs.

626 Background: First-line (1L) checkpoint inhibitor (CPI)-based combinations have become standard of care for patients with advanced renal cell carcinoma (aRCC). Data are required to inform optimal sequencing of aRCC therapies. CARINA is a non-interventional study of treatment sequencing and outcomes in patients with aRCC initiated on 1L CPI-based combination therapy. We report the results of a pre-planned interim analysis. Methods: We reviewed electronic prescribing records from participating UK specialist centers to identify patients (aged ≥ 18 years) with aRCC who received 2L therapy after 1L CPI-based combination therapy. The primary objective was to determine the treatment pathway for patients with aRCC who initiated treatment with a CPI-based combination and received subsequent therapy. Secondary objectives included treatment duration and objective response rate (ORR). Outcomes were evaluated for all patients (enrolled population [EP]) and for the patient subgroup who received 2L cabozantinib. Results: In total, 129 patients were eligible for inclusion in this interim analysis of the EP (mean [SD] age at diagnosis, 60.0 [9.9] years; 75.2% male; 77.3% clear-cell aRCC). Of these patients, 82.9% received 1L ipilimumab + nivolumab (Ipi + Nivo, n = 107) and 17.1% received axitinib + avelumab (Axi + Ave, n = 22); median (95% CI) duration of 1L treatment was 10.2 (9.1–17.1) weeks, ORR was 18.4%. The most commonly prescribed 2L therapies after Ipi + Nivo were cabozantinib (74.8%) and sunitinib (13.1%); the most commonly prescribed 2L therapies after Axi + Ave were lenvatinib + everolimus (45.5%) and cabozantinib (31.8%). Median (95% CI) duration of all 2L therapies was 23.6 (14.0–28.3) weeks, and median duration of 2L cabozantinib was 28.1 (20.1–37.1) weeks. ORR to 2L therapy was 30.4% for the EP, and 38.8% for the subgroup of patients who received 2L cabozantinib. Conclusions: In this interim analysis, the most commonly prescribed 2L therapies were cabozantinib and sunitinib after Ipi + Nivo, and lenvatinib + everolimus and cabozantinib after Axi + Ave. Antitumor response with 2L cabozantinib was observed after prior CPI-based therapy. Clinical trial information: NCT04957160 .

9527 Background: Combination of immune checkpoint inhibitors and targeted therapy may produce durable and deep response in a higher proportion of pts with BRAF V600–mutant unresectable or metastatic melanoma. A recent report from the randomized, double-blind, placebo (PBO)-controlled Part 3 of the Phase 3 COMBI-i trial (NCT02967692) failed to show a statistically significant progression-free survival (PFS) benefit (hazard ratio (HR) of 0.82 (95% CI, 0.66‒1.03, p=.042)). Here, we report 3-year OS data from COMBI-i part 3. Methods: Eligible pts were randomized 1:1 to receive either S+D+T (n = 267; S 400 mg IV Q4W + D 150 mg orally BID + T 2 mg orally QD) or PBO+D+T (n = 265), until progression or unacceptable toxicity. Although the primary endpoint of PFS was not met, exploratory OS and safety analyses were performed. OS was summarized descriptively using Kaplan–Meier methods and HR was estimated using a stratified cox regression model. Results: As of October 19, 2021 (median follow-up, 42.8 months), the median OS was not reached in S+D+T arm and was 40.4 months with PBO+D+T (HR 0.796; 95% CI, 0.615‒1.029). There were 113 (42.3%) deaths in the S+D+T and 126 (47.5%) in the PBO+D+T. Estimated 2-year and 3-year OS rates were 67.7% (95% CI 61.6‒73.1) and 60.1% (95% CI 53.8‒65.8) with S+D+T vs 61.9% (95% CI 55.6‒67.5) and 52.9% (95% CI 46.6‒58.9) with PBO+D+T, respectively. An OS benefit was observed with S+D+T in these prespecified subgroups – Eastern Cooperative Oncology Group Performance Status (ECOG PS) 1 (HR 0.50; 95% CI, 0.32‒0.8), age ≥65 years (HR 0.58; 95% CI, 0.36‒0.94), PD-L1 negative ( < 1%) (HR 0.62; 95% CI, 0.42‒0.91), sum of lesion diameters ≥ 66 mm at baseline (HR 0.63; 95% CI, 0.43‒0.91) and metastatic sites ≥ 3 (HR 0.66; 95% CI, 0.47‒0.94). Adverse events (AEs) irrespective of study treatment relationship were observed in 99.3% of pts in S+D+T vs 97.3% in PBO+D+T. The most common AEs (in > 30%; all grades) were pyrexia, diarrhea, and nausea. Grade ≥3 treatment-related AEs (TRAEs) occurred in 56.9% vs 35.2% of pts treated with S+D+T vs PBO+D+T, respectively. Dose reductions of D and T due to AEs were more frequent in the S+D+T arm than PBO+D+T arm (47.2% vs 25.4% and 45.7% vs 25.4%, respectively), contributing to a lower relative dose intensity; the TRAEs leading to discontinuation of all 3 study drugs occurred in 13.5% vs 8% of pts, respectively. Conclusions: Results from this landmark 3-year OS analysis from COMBI-i- part 3 was consistent with the primary analysis, while the PBO+D+T showed a higher OS rate than previously observed for D+T alone in COMBI D/V studies, with a longer median follow-up. Subgroup analyses showed that ECOG PS 1, age ≥65 years, negative PD-L1 status and high tumor burden were associated with better OS in S+D+T in terms of HR. Clinical trial information: NCT02967692.

9584 Background: All immune therapies that rapidly activate T cells, including T cell engagers, can induce cytokine release syndrome (CRS). Tebentafusp (tebe), a T cell receptor bispecific (gp100 x CD3) can also induce skin adverse events (AEs), due to gp100+ cutaneous melanocytes. CRS and skin AEs may require management with short term corticosteroids, which may also be used as premedication for subsequent tebe doses. Here we report the first analysis of systemic corticosteroid use and correlation with efficacy from a Phase (Ph) 3 trial for any T cell engager. Methods: Post hoc analyses were performed on the tebe arm of the Ph3 [NCT03070392] study in previously untreated HLA-A*02:01+ metastatic uveal melanoma (mUM) (N = 245). Due to the low rate of severe AEs in Ph1 trials, prophylactic corticosteroids were not mandated. The association between overall survival (OS) and corticosteroid use (new start within 30 days of first tebe dose) was investigated using landmark analyses in the safety population. Multivariate analyses were adjusted for key patient characteristics and AEs of special interest: CRS, rash, and liver function test (LFT) elevation. Steroid type (hydrocortisone vs. others) and treatment duration (1 vs. > 1 day) were also investigated. Results: In the Ph3 trial, 64/245 (26%) patients received new systemic corticosteroid within 30 days after the first dose of tebe, mostly for treatment of AEs (56/64, 88%) or pre-medication due to previous AE (14/64, 22%). 25 of the 64 patients received corticosteroids only for a single day. The most frequent AEs (≥15%) were rash (18/64, 28%), CRS (15/64, 23%), and hypotension (12/64, 19%). In a logistic regression model, elevated baseline LDH, the dominant prognostic marker, was most strongly associated with use of corticosteroids (p = 0.01). In the multivariate analysis, corticosteroids were not associated with any significant OS difference (HR 1.41, 95% CI 0.83-2.4, p = 0.2) and this effect did not differ in patients with or without CRS, rash or LFT elevation (all interaction tests p > 0.2). There was no difference in OS according to corticosteroid type or whether administered for 1 vs > 1 day. Conclusions: This is the first analysis from a phase 3 trial of the impact of systemic corticosteroids on survival for a T cell engaging cancer therapy. The vast majority of tebe-treated patients (84%) either did not require corticosteroids (74%) or only received them on a single day (10%). The most frequent reason for corticosteroid use was an emergent AE, including CRS and rash. Corticosteroid use following the pre-specified AE guidelines was not associated with any significant impact on OS. Clinical trial information: NCT03070392.

9563 Background: DMFS is an important endpoint for patients with stage III cutaneous melanoma, as delaying or preventing systemic disease is associated with improved clinical and patient-reported outcomes. Prior results from the phase 3 COMBI-AD trial (NCT01682083) showed 5-year DMFS rates of 65% with adjuvant D + T vs 54% with placebo (PBO; hazard ratio [HR] = 0.55; 95% CI: 0.44-0.70). An analysis of DMFS by AJCC-7 stages IIIA-C suggested a similar benefit of D + T vs PBO regardless of stage (Dummer R et al. N Engl J Med. 2020). Here, we report 5-year DMFS rates by AJCC-8 stages IIIA-D, other prognostic subgroups, and results of a regression tree analysis with DMFS. Methods: Patients with resected AJCC-7 stage III BRAFV600E/K-mutant melanoma were randomized to either D (150 mg twice daily) + T (2 mg once daily) or 2 matched PBOs for 12 months. Primary endpoint was relapse-free survival (RFS); DMFS was a secondary endpoint. Kaplan-Meier survival analyses were performed to assess the long-term benefits for DMFS rates with D + T vs PBO. The regression tree analysis (data cutoff: 5 years) for all patients (N = 870) evaluated potential prognostic/predictive factors of long-term DMFS including baseline age, sex, region, BRAF mutation type, body mass index, lactate dehydrogenase levels, ECOG, T and N categories, histology, primary tumor ulceration, treatment type, number of lymph nodes with metastases, tumor mutational burden, and interferon-gamma gene expression signature (IFN-γ GES). Results: At 5 years, DMFS rates were higher for patients with AJCC-8 stages IIIB-D disease receiving adjuvant D + T vs PBO (table). Five-year DMFS rates also favored D + T vs PBO in subgroups of patients with microscopic or macroscopic lymph node involvement (table) and those with or without primary tumor ulceration and/or in-transit metastases. A regression tree revealed T and N stage, treatment type, and IFN-γ GES as important variables defining 5-year DMFS subgroups. Conclusions: In this retrospective analysis, adjuvant D + T provided long-term DMFS benefit vs PBO in stage IIIB-D patients with resected BRAFV600E/K-mutant melanoma. Key clinical and patient factors impacting DMFS were similar to prior RFS findings (ESMO 2021; Robert C et al. Ann Oncol. 2021) and included T and N stage, treatment type, and IFN-γ GES. These results further validate the robust long-term clinical benefit of adjuvant D + T for patients with melanoma. Clinical trial information: NCT01682083. [Table: see text]

301 Background: The combination therapy avelumab + axitinib (A + Ax) has demonstrated superior progression-free survival (PFS) and objective response rate (ORR) benefit across all International Metastatic RCC Database Consortium (IMDC) risk groups (favourable, intermediate, and poor) vs sunitinib in patients with previously untreated aRCC. A + Ax is now approved and funded in the UK; on 29 October 2019, the European Commission approved A + Ax for first-line treatment of adult patients with aRCC, and it has been funded by the Cancer Drugs Fund since 30 July 2020. Here we report 12-month real-world outcomes of A + Ax in patients with aRCC in the UK. Methods: Patients ≥18 years with diagnosed aRCC who initiated A + Ax treatment outside of a clinical trial on or after 1 August 2019 via an early access to medicines scheme were recruited at 4 UK sites. Patient informed consent was obtained. Primary endpoints of interest include overall survival (OS), best response, PFS and ORR at 12 months. Descriptive statistics are provided. Recruitment is ongoing until Jan 2022 and follow-up until July 2023. Results: This analysis includes 36 patients with a minimum 12 month follow up. Median age at baseline was 66.2 (range, 39.8-84.1) years. 78% were male, 69% were White, and 6% were Asian/Asian British; ethnicities of 25% of patients were not recorded. Patient IMDC risk statuses were: 39% favourable, 42% intermediate, 17% poor, and 3% unknown; 89% had an ECOG PS of 0 or 1. Median time between aRCC diagnosis and A + Ax initiation was 1.8 months. Most patients had clear cell (72%) or other (25%) histology, had undergone nephrectomy (61%), and had 1 or 2 sites of metastatic disease (69%). The most common metastatic sites were lung (50%), bone (36%), and lymph node (25%). The 12 month OS rate was 86% (95% CI 74.8-97.4), and ORR was 53% (95% CI 36.5-69.1) with 6% achieving a complete response and 47% achieving partial response. Median duration of follow up and PFS was 12 months. Best responses within 12 months of observation were: complete response = 2 (6%), partial response = 17 (47%), stable disease = 14 (39%), and progressive disease = 3 (8%). At the time of the first and second infusions, 39% of patients received Ax at the starting dose of 5 mg twice daily, 47% had a dose escalation, and 14% had a dose reduction. Infusion-related reactions (IRRs) were recorded in 9 patients (25%) in the first 12 months, with 10 events total. All 10 IRRs required the use of high-dose corticosteroids. Median time from A + Ax initiation to IRR was 1.3 months. A + Ax was discontinued in 1 patient (3%) due to toxicity and 4 patients (11%) due to disease progression. Conclusions: In this real-world study of A + Ax treatment in the UK, A + Ax displayed comparable clinical responses to previously published data. OS, ORR, and best response figures were in line with published randomised controlled trials, which is encouraging in a nontrial population.

LBA8509 Background: Dacarbazine (D) and paclitaxel (P) have been used to treat MM pts with limited effect. The MM treatment landscape has recently changed with the approval of vemurafenib and ipilimumab in 2011, but secondary malignancies or other toxicities are of concerns. T is a reversible, highly selective allosteric inhibitor of MEK1/2 activation and kinase activity. In a PhII trial (NCT01037127), pts with BRAFV600E mutation MM had median PFS of 5.3 mos. This PhIII trial (NCT01245062) was conducted in pts with BRAFV600E/K mutant advanced or MM. Methods: Pts were randomized 2:1 to T (2mg QD) or C (D or P). Pts were stratified by baseline LDH level and prior C; pts in the C arm were allowed to crossover to receive T after confirmation of PD. Primary endpoint was PFS in pts with BRAFV600E mutation-positive MM and no prior brain mets; secondary endpoints were OS, ORR and safety in primary and ITT. PFS and OS were compared using a stratified log-rank test. The study was designed with ≥99% power and one-sided α = 0.025 to detect 57% reduction in the risk of PD or death in pts treated with T vs C. Results: Between Dec 2010 and Jul 2011, 322 pts were randomized to T (n=214) or C (n=108); 273 pts were BRAFV600E mutation-positive with no prior brain mets. HR for primary population for PFS by investigator was 0.44 (95% CI 0.31–0.64; pV600E/K mutant MM.