What the ATOMIC Trial Means for Stage III Colon Cancer

While results from the ATOMIC trial (NCT02912559) demonstrate a significant improvement in disease-free survival with the addition of atezolizumab to FOLFOX chemotherapy for stage III deficient mismatch repair (dMMR) colon cancer, treatment decisions still require individualized discussions with patients. In an interview with Targeted Oncology, Francis Sinicrope, MD, gastrointestinal oncologist at Mayo Clinic, discusses how patient risk, chemotherapy duration, and evolving survival data influence treatment planning in the adjuvant setting.

Watch the interview with Dr. Sinicrope.

Sinicrope noted that the ATOMIC trial enrolled patients with stage III dMMR colon cancer and demonstrated an approximately 50% reduction in recurrence or death for those who received atezolizumab in addition to standard FOLFOX chemotherapy. He described the findings as practice changing, noting that the combination regimen is now considered a standard treatment option for this patient population.

From a clinical perspective, the benefit of adding immunotherapy appeared consistent across all subgroups analyzed in the trial, including both high-risk and low-risk stage III patients. This broad applicability supports the use of atezolizumab across the dMMR population rather than limiting its use to select patients based on risk classification alone.

Questions remain around chemotherapy duration within the regimen. Sinicrope noted that patients appear to need at least three months of chemotherapy to derive maximum benefit from the combination, with some evidence suggesting that longer duration may provide additional advantage. This finding indicates that immunotherapy alone may not be sufficient in this setting, and that the chemotherapy backbone plays an important role in optimizing outcomes.

Overall survival data from the ATOMIC trial remain premature. Because patients who experience recurrence often go on to receive immunotherapy as a subsequent line of therapy, interpreting differences in overall survival between the treatment arms may prove difficult as follow-up continues to mature.

Ultimately, Sinicrope emphasized that the survival curves from the ATOMIC trial show a plateauing effect, suggesting that more patients may be achieving long-term cure with the addition of immunotherapy. His perspective is that clinicians should consider patient risk profile, willingness to complete the recommended chemotherapy course, and long-term treatment goals when incorporating these findings into frontline treatment planning for stage III dMMR colon cancer.