ATOMIC (Alliance A021502)
Adding a year of immunotherapy to chemotherapy after surgery halved recurrences in stage III colon cancers with a broken DNA spell-checker.
ASCO 2025 plenary: 3-year DFS 86.4% vs 76.6% (HR 0.50). The first phase 3 to show immunotherapy benefit in the adjuvant colon setting; establishes a new standard for the ~10-15% of stage III colon cancers that are dMMR. Whether chemotherapy is needed at all in this group (NICHE-2 logic) is the next question.
Setting
Resected stage III dMMR colon cancer: adjuvant FOLFOX + atezolizumab (12 months) vs FOLFOX
Phase
Phase 3
Sponsor
Alliance / NCI
Registry
Headline result
3-year DFS 86.4% vs 76.6%, HR 0.50.
Reported
2025
Enrolled
712
Replication
First and only randomised adjuvant IO trial in dMMR colon cancer; consistent in direction with NICHE-2 and the metastatic trials.
In plain words
What these results mean for people, not percentages
Disease-free survival at 3 yearsprimarysurrogate endpoint
- 86.4 vs 76.6 out of 100 alive without the cancer coming back at 3 years with FOLFOX + atezolizumab compared with FOLFOX; 9.8 more per 100.
- Roughly one extra person helped for every 10 treated. That is a rough figure taken from the two percentages, not a guarantee for any one person.
- Put another way, the treated group had about 50 percent lower chance of the event at any given time (hazard ratio 0.5, likely range 0.34 to 0.72).
- This is a surrogate endpoint: it measures the cancer being controlled or absent on scans and tests, which often, but not always, translates into living longer.
- These results apply to the people the trial enrolled: Resected stage III dMMR colon cancer: adjuvant FOLFOX + atezolizumab (12 months) vs FOLFOX. People in a different situation may not see the same effect.
- The trial selected people by a biomarker (dMMR); the result should not be assumed for people whose cancer does not have it.
Numbers are from the trial as recorded here; see the source links in the table below. This is orientation, not medical advice: ask your team how closely the trial population matches you.
712 participants enrolled.
Disease-free survival at 3 yearsprimary
HR 0.5 (0.34–0.72)
FOLFOX + atezolizumab
86.4 mo
FOLFOX
76.6 mo
| Endpoint | Arm | n | Value | HR (95% CI) | p | Source |
|---|---|---|---|---|---|---|
| Disease-free survival at 3 yearsprimary | FOLFOX + atezolizumab | 355 | 86.4 percent | 0.5 (0.34–0.72) | — | link |
| FOLFOX | 357 | 76.6 percent |
Replication
First and only randomised adjuvant IO trial in dMMR colon cancer; consistent in direction with NICHE-2 and the metastatic trials.