The FDA has approved atezolizumab (Tecentriq) in combination with a fluoropyrimidine and oxaliplatin as the first-ever adjuvant immunotherapy regimen for stage III mismatch repair–deficient (dMMR) colon cancer — a meaningful leap forward for patients who've undergone surgery and need to prevent recurrence. A subcutaneous formulation (Tecentriq Hybreza) was also approved for eligible patients aged 12 and older.

The approval is backed by the phase 3 ATOMIC trial, led by Mayo Clinic's Dr. Frank Sinicrope through the Alliance for Clinical Trials in Oncology. The trial enrolled 712 patients with completely resected stage III dMMR colon cancer, randomizing them to receive either atezolizumab plus mFOLFOX6 chemotherapy or chemotherapy alone. Previously, adjuvant treatment hadn't been tailored based on mismatch repair status — this changes that.

By the Numbers:

• 50% reduction in risk of disease recurrence or death with atezolizumab + chemo vs. chemo alone (HR 0.50)
• 86.3% 3-year disease-free survival in the atezolizumab arm vs. 76.2% in the chemo-only arm
• ~15% of all colon cancers have dMMR; more than 25% of ATOMIC enrollees were under age 50
• 712 patients enrolled across the U.S. and Germany

Why it matters: dMMR colon cancer disproportionately affects younger adults and those with Lynch syndrome. By moving immunotherapy earlier — right after surgery — clinicians can now target residual microscopic cancer cells before recurrence, potentially adding decades of life for younger patients. This FDA approval makes the regimen broadly accessible and sets a new standard of care.