Multicenter phase 3 trial of atezolizumab plus mFOLFOX6 for stage III mismatch repair-deficient colon cancer

Standard adjuvant chemotherapy for stage III colon cancer consists of a fluoropyrimidine plus oxaliplatin regimen. The multicenter phase 3 ATOMIC trial in the US evaluated addition of atezolizumab (anti-PD-1) to mFOLFOX6 in patients with stage II colon cancer with mismatch repair-deficient (dMMR) status. Patients were randomized (1:1) to adjuvant atezolizumab plus mFOLFOX for 6 months followed by atezolizumab monotherapy for another 6 months (n=355) or mFOLFOX alone for 6 months (n=357). The primary endpoint was disease-free survival (DFS). At a median follow-up of 40.9 months, the 3-year DFS rate was 86.3% in the atezolizumab-mFOLFOX6 group and 76.2% in the mFOLFOX6 group (HR 0.50; p<0.001). Adverse events of grade 3 or 4 occurred in 84.1% of patients in the atezolizumab-mFOLFOX6 group and 71.9% of patients in the mFOLFOX6 alone group. The authors conclude that the addition of atezolizumab to mFOLFOX6 significantly improved DFS among patients with stage III dMMR colon cancer.