Overall survival (OS) with first-line atezolizumab (A) or placebo (P) in combination with vemurafenib (V) and cobimetinib (C) in BRAFV600 mutation-positive advanced melanoma: Second interim OS analysis of the phase 3 IMspire150 study.

9547 Background: Primary analysis of the phase 3 IMspire150 study (NCT02908672) demonstrated improved investigator-assessed progression-free survival (PFS) with first-line A + V + C vs P + V + C in patients (pts) with BRAFV600 mutation–positive advanced melanoma (hazard ratio [HR] 0.78; 95% CI, 0.63-0.97; P= 0.025). With median follow-up of 18.9 months at primary analysis, OS data were immature; interim analysis of OS at the time of the primary analysis demonstrated a trend in favor of A + V + C over P + V + C (estimated 2-year OS rate, 60.4% vs 53.1%) (Gutzmer et al. Lancet 2020;395:1835-1844). Herein, we present results from the second interim OS analysis of the IMspire150 study. Methods: IMspire150 enrolled previously untreated pts with stage IV or unresectable stage IIIc BRAFV600 mutation-positive melanoma (n = 514). Pts were randomized 1:1 to receive 28-day cycles of A + V + C (n = 256) or P + V + C (n = 258). Pts received V + C in cycle 1; A or P was added on days 1 and 15 from cycle 2 onwards. The second interim OS analysis was planned after ̃270 OS events were recorded, and was projected to have a minimally detectable difference of HR of 0.74 with a P value boundary of 0.0140. OS was estimated using the Kaplan-Meier method. Results: At data cutoff (Sept 8, 2021), 273 OS events had occurred. Median follow-up was 29.1 months (range, 1-54) for A + V + C and 22.8 months (range, 0-54) for P + V + C. A continued trend toward OS benefit in favor of A + V + C over P + V + C was observed with median OS of 39.0 vs 25.8 months, but the difference did not reach statistical significance (HR, 0.84; 95% CI, 0.66-1.06; P= 0.1432). A delayed treatment effect was observed, with landmark OS rates for A + V + C vs P + V + C of 76.1% vs 76.5% at 12 months and 61.5% vs 53.3% at 24 months. With additional follow-up, A + V + C continued to show PFS benefit over P + V + C (HR, 0.79; 95% CI, 0.64-0.97; P= 0.0224); overall response rates (66.7% vs 65.0%) and median duration of response (21.0 vs 12.6 months) remained consistent with those reported at primary analysis. No new safety signals were observed with additional follow-up. Conclusions: With further follow-up, A + V + C demonstrated a consistent, but not statistically significant, improvement in OS and continued benefit in duration of response versus P + V + C in previously untreated pts with BRAFV600 mutation–positive advanced melanoma. Clinical trial information: NCT02908672.