Top Line: As presented at ASCO last year, adjuvant chemoimmunotherapy is the new standard for stage III deficient mismatch repair (dMMR) colon cancer.
The Study: We now have the full publication of the phase 3 ATOMIC trial that randomized 712 patients with resected deficient mismatch repair (dMMR) stage III colon cancer to standard adjuvant mFOLFOX6 × 12 cycles (6 months) ± atezolizumab (given concurrently then continued for 12 months total). At a median follow-up of 3.5 years, the primary endpoint was met at interim analysis: 3-year disease-free survival improved from 76% with chemo alone to 86% with chemoimmunotherapy (HR 0.50, p<0.001). Interestingly, benefit appeared most pronounced in patients receiving >6 cycles (>3 months) of FOLFOX (HR 0.41), supporting the oft-questioned utility of a “chemo backbone.” Overall survival data remain immature (HR 0.90), with any potential discrepancy likely diminished by high rates of salvage immunotherapy at recurrence. Toxicity was higher with atezo (grade 3–4 events 84% vs 72%), with expected bumps in fatigue, neutropenia, and low-grade immune-related events.
TBL: “These findings support universal MMR testing in all patients with newly diagnosed colon cancer, both to identify Lynch syndrome and to determine eligibility for immunotherapy.” | Sinicrope, N Engl J Med 2026
The Study: We now have the full publication of the phase 3 ATOMIC trial that randomized 712 patients with resected deficient mismatch repair (dMMR) stage III colon cancer to standard adjuvant mFOLFOX6 × 12 cycles (6 months) ± atezolizumab (given concurrently then continued for 12 months total). At a median follow-up of 3.5 years, the primary endpoint was met at interim analysis: 3-year disease-free survival improved from 76% with chemo alone to 86% with chemoimmunotherapy (HR 0.50, p<0.001). Interestingly, benefit appeared most pronounced in patients receiving >6 cycles (>3 months) of FOLFOX (HR 0.41), supporting the oft-questioned utility of a “chemo backbone.” Overall survival data remain immature (HR 0.90), with any potential discrepancy likely diminished by high rates of salvage immunotherapy at recurrence. Toxicity was higher with atezo (grade 3–4 events 84% vs 72%), with expected bumps in fatigue, neutropenia, and low-grade immune-related events.
TBL: “These findings support universal MMR testing in all patients with newly diagnosed colon cancer, both to identify Lynch syndrome and to determine eligibility for immunotherapy.” | Sinicrope, N Engl J Med 2026