Purpose: To report the 5-year overall survival (OS) landmark and the long-term safety profile of vemurafenib plus cobimetinib (BRAF plus MEK inhibition, respectively) in the BRIM7 study. Patients and Methods: Thisphase Ib, dose-finding, and expansion study evaluated combination treatment with vemurafenib and cobimetinib in two cohorts of patients with advanced BRAF V600-mutated melanoma: patients who were BRAF inhibitor (BRAFi)-naïve (n ¼ 63) or patients who had progressed on prior treatment with BRAFi monotherapy [vemurafenib monotherapy-progressive disease (PD); n ¼ 66]. Patients in the dose-escalation phase received vemurafenib at 720 or 960 mg twice daily in combination with cobimetinib at 60, 80, or 100 mg/d for 14 days on/14 days off, 21 days on/7 days off, or continuously. Two regimens were selected for expansion: vemurafenib (720 and 960 mg twice daily) and cobimetinib (60 mg/d 21/7). Results: Median OS was 31.8 months [95% confidence interval (CI), 24.5-not estimable] in the BRAFi-naïve cohort. The landmark OS rate plateaued at 39.2% at years 4 and 5 of follow-up. In the vemurafenib monotherapy-PD cohort, the median OS was 8.5 months (95% CI, 6.7-11.1), and the landmark OS rate plateaued at 14.0% from 3 years of follow-up. No increase was observed in the frequency and severity of adverse events with long-term follow-up. No new toxicities were detected, and there was no increase in the frequency of symptomatic MEK inhibitor class-effect adverse events. Conclusions: A subset of patients with advanced BRAF V600mutated melanoma treated with a combination regimen of vemurafenib and cobimetinib achieve favorable long-term outcomes.

• Despite strong preclinical rationale, combined cobimetinib-mediated MEK inhibition and GDC-0994-mediated ERK inhibition was not tolerable on two 28-day dosing schedules in which GDC-0994 was given for 21 days continuously and cobimetinib administered over 21 days either continuously or intermittently. • Adverse events were as expected for mitogen-activated protein kinase pathway inhibition, but overlapping and cumulative toxicities could not be managed on either dosing schedule. • Pharmacokinetic parameters of cobimetinib and GDC-0994 given in combination were similar to those previously observed in monotherapy studies, so that there was no evidence of drug-drug interaction. • Cycle 1 metabolic responses were observed by 18F-fluorodeoxyglucose-positron emission tomography but were not predictive of outcome measured by RECIST 1.1.

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