ATOMIC Trial: Atezolizumab Improves DFS in dMMR Colon Cancer
Arturo Loaiza-Bonilla, MD, MSEd, discusses the phase 3 ATOMIC trial presented at the 2025 American Society of Clinical Oncology Annual Meeting.
Arturo Loaiza-Bonilla, MD, MSEd, systemwide chief of hematology and oncology at St. Lukes University Heath Network and co-founder and chief medical officer at Massive Bio, discusses the phase 3 ATOMIC trial (NCT02912559), presented at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting.1
The study evaluated the addition of atezolizumab (Tecentriq) to standard mFOLFOX6 chemotherapy in patients with resected stage III colon cancer characterized by deficient mismatch repair (dMMR). The study demonstrated a statistically significant and clinically meaningful improvement in disease-free survival (DFS), establishing a potential new standard of care for this patient population.
In this multicenter trial, 712 patients with dMMR stage III colon cancer were randomized following surgery to receive either mFOLFOX6 plus atezolizumab followed by maintenance atezolizumab for 6 months, or mFOLFOX6 alone. Patients had not received prior chemotherapy or radiation and had ECOG performance status of 0 to 2. The primary end point was DFS, with secondary end points including overall survival and safety.
At a median follow-up of 37.2 months, and at the second interim analysis, the trial met the pre-specified efficacy boundary. The 3-year DFS rate was 86.4% for the atezolizumab arm vs 76.6% for chemotherapy alone (HR, 0.50; 95% CI, 0.34-0.72; P <.0001), indicating a 50% reduction in the risk of recurrence or death. The benefit was consistent across subgroups, including age, sex, race, tumor location, T-stage, and risk category.
Safety findings were consistent with the known profiles of both agents. The combination was associated with a manageable increase in nonfebrile neutropenia but no new safety signals.
ATOMIC is the first phase 3 trial to demonstrate the benefit of adding immunotherapy in the adjuvant setting for colon cancer. The results support the integration of atezolizumab into first-line treatment for patients with dMMR stage III disease and represent a step forward in tailoring adjuvant therapy based on tumor biology. The trial was conducted across more than 300 sites within the National Clinical Trials Network and was supported by the National Cancer Institute and cooperative group infrastructure.
