Atezolizumab plus FOLFOX for Stage III Mismatch Repair–Deficient Colon Cancer

BACKGROUND: Standard adjuvant chemotherapy for stage III colon cancer consists of a fluoropyrimidine-plus-oxaliplatin regimen. Whether the addition of atezolizumab (an anti-programmed death ligand 1 agent) to a modified FOLFOX6 regimen (fluorouracil, oxaliplatin, and leucovorin; called mFOLFOX6) would improve outcomes in patients with stage III colon cancer with mismatch repair-deficient (dMMR) status is unclear. METHODS: In a phase 3 trial, we randomly assigned, in a 1:1 ratio, patients with resected stage III dMMR tumors to receive either adjuvant atezolizumab plus mFOLFOX6 for 6 months, with atezolizumab continued as monotherapy (for a total of 12 months of therapy), or mFOLFOX6 alone for 6 months. The primary end point was disease-free survival. Secondary end points were overall survival and the adverse-event profile. RESULTS: A total of 355 patients were assigned to receive atezolizumab plus mFOLFOX6 and 357 to receive mFOLFOX6 alone. The median age of the patients was 64 years, 55.1% were women, and 53.9% had tumors that were T4, N2, or both (indicating high risk). At a median follow-up of 40.9 months, the 3-year disease-free survival was 86.3% (95% confidence interval [CI], 81.8 to 89.8) in the atezolizumab-mFOLFOX6 group, as compared with 76.2% (95% CI, 70.9 to 80.6) in the mFOLFOX6 group (hazard ratio for disease recurrence or death, 0.50; 95% CI, 0.35 to 0.73; P<0.001). Adverse events of grade 3 or 4 occurred in 84.1% of the patients who received atezolizumab plus mFOLFOX6 and in 71.9% of those who received mFOLFOX6 alone. CONCLUSIONS: The addition of atezolizumab to mFOLFOX6 significantly improved disease-free survival among patients with stage III dMMR colon cancer. (Funded by the National Cancer Institute of the National Institutes of Health and Genentech; ATOMIC ClinicalTrials.gov number, NCT02912559.).