Nivolumab plus ipilimumab versus nivolumab in microsatellite instability-high metastatic colorectal cancer (CheckMate 8HW): a randomised, open-label, phase 3 trial

Background CheckMate 8HW prespecified dual primary endpoints, assessed in patients with centrally confirmed microsatellite instability-high or mismatch repair-deficient status: progression-free survival with nivolumab plus ipilimumab compared with chemotherapy as first-line therapy and progression-free survival with nivolumab plus ipilimumab compared with nivolumab alone, regardless of previous systemic treatment for metastatic disease. In our previous report, nivolumab plus ipilimumab showed superior progression-free survival versus chemotherapy in first-line microsatellite instability-high or mismatch repair-deficient metastatic colorectal cancer in the CheckMate 8HW trial. Here, we report results from the prespecified interim analysis for the other primary endpoint of progression-free survival for nivolumab plus ipilimumab versus nivolumab across all treatment lines. Methods CheckMate 8HW is a randomised, open-label, international, phase 3 trial at 128 hospitals and cancer centres across 23 countries. Immunotherapy-naive adults with unresectable or metastatic colorectal cancer across different lines of therapy and microsatellite instability-high or mismatch repair-deficient status per local testing were randomly assigned (2:2:1) to nivolumab plus ipilimumab (nivolumab 240 mg, ipilimumab 1 mg/kg, every 3 weeks for four doses; then nivolumab 480 mg every 4 weeks; all intravenously), nivolumab (240 mg every 2 weeks for six doses, then 480 mg every 4 weeks; all intravenously), or chemotherapy with or without targeted therapies. The dual independent primary endpoints were progression-free survival by blinded independent central review with nivolumab plus ipilimumab versus chemotherapy (first line) and progression-free survival by blinded independent central review with nivolumab plus ipilimumab versus nivolumab (all lines) in patients with centrally confirmed microsatellite instability-high or mismatch repair-deficient metastatic colorectal cancer. This study is registered with ClinicalTrials. gov (NCT04008030). Findings Between Aug 16, 2019, and April 10, 2023, 707 patients were randomly assigned to nivolumab plus ipilimumab (n=354) or nivolumab alone (n=353). 296 (84%) of 354 patients in the nivolumab plus ipilimumab group and 286 (81%) of 353 patients in the nivolumab group were centrally confirmed to have microsatellite instability-high or mismatch repair-deficient status. At the data cutoff on Aug 28, 2024, median follow-up (from randomisation to data cutoff) was 47<middle dot>0 months (IQR 38<middle dot>4 to 53<middle dot>2). Nivolumab plus ipilimumab treatment showed significant and clinically meaningful improvement in progression-free survival versus nivolumab (hazard ratio 0<middle dot>62, 95% CI 0<middle dot>48-0<middle dot>81; p=0<middle dot>0003). Median progression-free survival was not reached with nivolumab plus ipilimumab (95% CI 53<middle dot>8 to not estimable) and was 39<middle dot>3 months with nivolumab (22<middle dot>1 to not estimable). Treatment-related adverse events of any grade occurred in 285 (81%) of 352 patients receiving nivolumab plus ipilimumab and in 249 (71%) of 351 patients receiving nivolumab; grade 3 or 4 treatment-related adverse events occurred in 78 (22%) and 50 (14%) patients, respectively. There were three treatment-related deaths: one event of myocarditis and pneumonitis each in the nivolumab plus ipilimumab group and one pneumonitis event in the nivolumab group. Interpretation Nivolumab plus ipilimumab showed superior progression-free survival versus nivolumab across all treatment lines, with a manageable safety profile, in patients with microsatellite instability-high or mismatch repair- deficient metastatic colorectal cancer. These results, together with the first-line results of superior progression-free survival with nivolumab plus ipilimumab versus chemotherapy, suggest nivolumab plus ipilimumab as a potential new standard of care for patients with microsatellite instability-high or mismatch repair-deficient metastatic colorectal cancer.