At the ESMO GI Cancers Congress 2026, Anke Reinacher-Schick presented a secondary analysis from ATOMIC, evaluating whether the duration of adjuvant mFOLFOX6 chemotherapy or atezolizumab influenced disease-free survival in patients with stage III deficient mismatch repair colon cancer.
The presentation, titled “ATOMIC (A021502/AIO-KRK-0317): Does duration of adjuvant chemotherapy (chemo) or immunotherapy matter?” was presented as abstract 1O.
Background
ATOMIC previously showed that adding atezolizumab to adjuvant mFOLFOX6 significantly improved disease-free survival compared with mFOLFOX6 alone in patients with stage III deficient mismatch repair colon cancer.
In the main ATOMIC approach, patients received 6 months of mFOLFOX6, with or without 12 months of atezolizumab.
This secondary analysis focused on a practical question from the trial: whether disease-free survival was influenced by the number of mFOLFOX6 cycles received, and whether longer atezolizumab exposure added further benefit.
ATOMIC Trial Analysis
The analysis used a 6-month landmark and included patients who received at least one treatment cycle and were alive and disease-free at 6 months. Investigators compared patients who received 6 or fewer cycles of mFOLFOX6 with those who received more than 6 cycles. The number of mFOLFOX6 cycles was also assessed as a continuous variable.
For atezolizumab, the analysis compared patients who received fewer than 12 cycles with those who received 12 or more cycles. Analyses were adjusted for T stage and N stage.
The trial is identified as A021502/AIO-KRK-0317.
Read more about ATOMIC Trial Updates on OncoDaily.
Results
Among patients who received 6 or fewer cycles of mFOLFOX6, 3-year disease-free survival was similar between treatment arms. The rate was 80.0% with atezolizumab plus mFOLFOX6 and 79.9% with mFOLFOX6 alone (aHR 0.84; 95% CI: 0.35–2.01).
In contrast, among patients who received more than 6 cycles of mFOLFOX6, the atezolizumab-containing arm showed higher 3-year disease-free survival. The rate was 88.2% with atezolizumab plus mFOLFOX6 compared with 79.1% with mFOLFOX6 alone (aHR 0.45; 95% CI: 0.29–0.71).
In the atezolizumab-containing arm, disease-free survival was also assessed by FOLFOX duration. Patients who received more than 6 cycles of FOLFOX plus atezolizumab had numerically better DFS than those who received 6 or fewer cycles, with an adjusted HR of 0.54 (95% CI: 0.25–1.17).
Atezolizumab continuation after FOLFOX discontinuation differed by chemotherapy duration: 48% in the 6-or-fewer-cycle group and 87% in the more-than-6-cycle group.
For atezolizumab duration, 3-year disease-free survival was 84.0% among patients who received fewer than 12 cycles and 88.0% among those who received 12 or more cycles (aHR 0.81; 95% CI: 0.38–1.71; p=0.5807).
Conclusion
This retrospective exploratory analysis from ATOMIC suggests that the disease-free survival benefit of adding atezolizumab was detectable in patients who received more than 6 cycles of mFOLFOX6, but not in those who received 6 or fewer cycles.
The DFS benefit of atezolizumab plus FOLFOX appeared to increase with a greater number of FOLFOX cycles. For atezolizumab duration, outcomes were numerically better with 12 or more cycles, but this comparison did not show a clear additional DFS benefit over fewer cycles. The analysis was exploratory and was not powered to assess treatment duration effects in high-risk versus low-risk tumors.
Expert Highlights
Sharlene Gill, MD, MPH, MBA, FASCO, shared the ATOMIC duration analysis on X, highlighting the uncertainty around chemotherapy and immunotherapy duration in this exploratory analysis.
“Proferred Session
-ATOMIC (pH3 FOLFOX +/- atezo in dMMR stage 3 colon CA) duration of AT exploratory analysis
<20% of pts received <= 6cy FOLFOX
duration of FOLFOX appears to be associated with greater benefit with atezo…doesn’t answer if 3mos CAPOX sufficient?
<12cy vs >12cy atezo appears comparable but likely confounded by reasons for ICI d/c ?IRAE
I may be more confused now…clinical judgement is required!”
Arndt Vogel also shared the ATOMIC analysis on X, noting the apparent relationship between longer chemotherapy duration and greater atezolizumab benefit.
“ATOMIC (A021502/AIO-KRK-0317): Does duration of adjuvant CTx or immunotherapy matter?
surprising,benefit of atezo increased in pts receiving longer CTx
we need to balance tox and efficacy”
More details are available in the official ESMO Gastrointestinal Cancers Congress 2026 programme.