Background: Primary analysis of the phase 3 IMspire150 study showed improved investigator-assessed progression-free survival with first-line atezolizumab, vemurafenib, and cobimetinib (atezolizumab group) versus placebo, vemurafenib, and cobimetinib (control group) in patients with BRAF V600 mutation-positive melanoma. With a median follow-up of 18·9 months (IQR 10·4-23·8) at the primary analysis, overall survival data were immature. Here, we report the results from the second, prespecified, interim overall survival analysis., Methods: The multicentre, double-blind, placebo-controlled, randomised, phase 3 IMspire150 study was done at 108 academic and community hospitals in 20 countries. Patients aged 18 years or older with previously untreated unresectable stage IIIc or stage IV melanoma and an Eastern Cooperative Oncology Group performance status of 0 or 1 were eligible for inclusion. Patients were randomly assigned (1:1) to receive either atezolizumab (840 mg intravenously on day 1 and 15) or placebo plus vemurafenib (960 mg or 720 mg twice daily orally) and cobimetinib (60 mg once daily orally; 21 days on and 7 days off) in 28-day cycles. Atezolizumab and placebo were added to treatment regimens from cycle two onwards. Randomisation was done centrally (Durham, NC, USA) based on a permuted block randomisation scheme (block size of 4) using an interactive web-based response system and was stratified by geographical region and baseline lactate dehydrogenase concentration. Overall survival was analysed in the intention-to-treat population and safety was analysed in all patients who received at least one dose of study drug according to actual treatment received. The primary endpoint was investigator-assessed progression-free survival, which was previously reported. Here, we report the second, prespecified, interim overall survival analysis, which was planned after about 270 overall survival events had occurred. The trial is ongoing, but is no longer enrolling patients, and it is registered with ClinicalTrials.gov, NCT02908672., Findings: Between Jan 13, 2017, and April 26, 2018, 514 patients (median age 54 years [IQR 43-63]; 299 [58%] men and 215 [42%] women) were enrolled in the trial and randomly assigned to the atezolizumab group (256 [50%] patients) or the control group (258 [50%] patients). At the data cutoff (Sept 8, 2021), 273 patients had died (126 in the atezolizumab group and 147 in the control group). Median follow-up was 29·1 months (IQR 10·1-45·4) for the atezolizumab group versus 22·8 months (10·6-44·1) for the control group. Median overall survival was 39·0 months (95% CI 29·9-not estimable) in the atezolizumab group versus 25·8 months (22·0-34·6) in the control group (HR 0·84 [95% CI 0·66-1·06]; p=0·14). The most common adverse events of any grade in the atezolizumab group were blood creatine phosphokinase increased (123 [53%] of 231 patients), diarrhoea (116 [50%]), and pyrexia (115 [50%]). The most common adverse events of any grade in the control group were diarrhoea (157 [56%] of 280 patients), blood creatine phosphokinase increased (135 [48%]), and rash (119 [43%]). The most common grade 3-4 adverse events were increased lipase (54 [23%] of 231 patients in the atezolizumab group vs 62 [22%] of 280 patients in the control group), increased blood creatine phosphokinase (51 [22%] vs 50 [18%]), and increased alanine aminotransferase (32 [14%] vs 26 [9%]). Serious adverse events were reported in 112 (48%) patients in the atezolizumab group and 117 (42%) patients in the control group. Grade 5 adverse events were reported in eight (3%) patients in the atezolizumab group versus six (2%) patients in the control group. Two grade 5 adverse events (hepatitis fulminant and hepatic failure) in the atezolizumab group were considered to be associated with the triplet combination, and one event in the control group (pulmonary haemorrhage) was considered to be associated with cobimetinib., Interpretation: Additional follow-up of the IMspire150 trial showed that overall survival was not significantly improved with atezolizumab, vemurafenib, and cobimetinib compared with placebo, vemurafenib, and cobimetinib in patients with BRAF V600 mutation-positive advanced melanoma. Results of the final analysis are awaited to establish whether a significant improvement in overall survival can be achieved with long-term treatment with this triplet combination versus vemurafenib plus cobimetinib., Funding: F Hoffmann-La Roche., Competing Interests: Declaration of interests PAA reports grants from Bristol Myers Squibb, Roche/Genentech, Pfizer/Array, and Sanofi; consulting fees from Bristol Myers Squibb, Roche/Genentech, Merck Sharp & Dohme, Novartis, Merck Serono, Pierre Fabre, Sun Pharma, Sanofi, Idera, Sandoz, 4SC, Italfarmaco, Nektar, Pfizer/Array, Lunaphore, Medicenna, Bio-Al Health, ValoTx, and Replimmune; travel support from Pfizer; and advisory board member for Bristol Myers Squibb, Roche/Genentech, Merck Sharp & Dohme, Novartis, AstraZeneca, Immunocore, Boehringer-Ingelheim, Eisai, Regeneron, Daiichi Sankyo, Oncosec, Nouscom, Seagen, and iTeos. HG reports honoraria from Bristol Myers Squibb, MSD Oncology, Pierre Fabre, and Sanofi/Regeneron; research funding from Bristol Myers Squibb, Roche, MSD Oncology, Amgen, Novartis, and Iovance Biotherapeutics; travel, accommodation, and expenses from Bristol Myers Squibb, Merck Sharp & Dohme, Amgen, and Pfizer; and a consulting or advisory role for Bristol Myers Squibb, MSD Oncology, Amgen, Pierre Fabre, and Sanofi/Regeneron. CR reports consulting fees from Roche, Novartis, Pierre Fabre, MSD, Bristol Myers Squibb, Sanofi, Pfizer, and AstraZeneca; and payment or honoraria from Roche, Novartis, Pierre Fabre, MSD, Bristol Myers Squibb, Sanofi, Pfizer, and AstraZeneca. KL reports honoraria from Array Biopharma and Iovance Biotherapeutics; a consulting or advisory role for Array Biopharma, Iovance Biotherapeutics, Merck, Nektar, Regeneron, Roche, and Sanofi; research funding from Alkermes, Amgen, Array Biopharma, Bristol Myers Squibb, Incyte, Iovance Biotherapeutics, Kartos Therapeutics, Merck, Nektar, Neon Therapeutics, OncoSec, Regeneron, Replimune, Roche/Genentech, Seagen, Senhwa Biosciences, and Ultimovacs; and travel, accommodations, or expenses from Alkermes, Merck, Neon Therapeutics, Regeneron, and Roche/Genentech. SP reports honoraria from Biocad, Roche, Bristol Myers Squibb, and Merck Sharp & Dohme; speakers bureau for Biocad, Roche, Bristol Myers Squibb, and Merck Sharp & Dohme; and research funding from Roche, Merck Sharp & Dohme, Amgen, Novartis, Bristol Myers Squibb, and Biocad. RPP reports speakers bureau for Roche and Bristol Myers Squibb and research funding from Roche, Bristol Myers Squibb, Merck Sharp & Dohme, Bayer, and AstraZeneca. TE reports a consulting or advisory role for Bristol Myers Squibb/Medarex, Sanofi/Regeneron, Novartis, and Pierre Fabre and speakers bureau for Almirall Hermal. PR reports honoraria from Bristol Myers Squibb, MSD, Novartis, Roche, Pfizer, Pierre Fabre, Sanofi, and Merck; speaker's bureau for Pfizer, Novartis, and Pierre Fabre; consulting fee from Blueprint Medicines, Bristol Myers Squibb, MSD, Novartis, Pierre Fabre, and Philogen; research funding from Bristol Myers Squibb, Novartis, and Roche; and travel, accommodations, or expenses from Orphan Europe and Pierre Fabre. LD reports honoraria from Roche, Merck Sharp & Dohme, Bristol Myers Squibb, and Novartis and research funding from Roche, Merck Sharp & Dohme, Bristol Myers Squibb, Novartis, and Amgen. NZ reports honoraria from Roche, Novartis, Bristol Myers Squibb/Celgene, MSD Oncology, and AstraZeneca/Merck; consulting fees from Roche, MSD Oncology, Merck; and travel and accommodation expenses from MSD Oncology and Roche. JS reports a consultant or advisory role for Merck Sharp & Dohme and Bristol Myers Squibb. YY and IC report employment with Genentech and stock or other ownership with Roche/Genentech. CH and CX report employment with Roche. LK reports employment and ownership non-voting shares for Roche. GAM reports research funding to his institution from Genentech/Roche and Bristol Myers Squibb. RG reports honoraria from Bristol Myers Squibb, Merck Sharp & Dohme, Roche/Genentech, Novartis, Merck Serono, Almirall Hermal, Amgen, Sun Pharma, Pierre Fabre, Sanofi/Regeneron, and Immunocore; a consulting or advisory role for Bristol Myers Squibb, Merck Sharp & Dohme, Roche/Genentech, Novartis, Almirall Hermal, 4SC, Amgen, Pierre Fabre, Merck Serono, Sun Pharma, Sanofi, and Immunocore; research funding from Pfizer, Novartis, Johnson & Johnson, Amgen, Merck Serono, Sun Pharma, and Sanofi; and travel, accommodations, or expenses from Bristol Myers Squibb, Roche, Merck Serono, Pierre Fabre, and Sun Pharma. DS declares no competing interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)