Study Finds Atezolizumab Plus Chemotherapy Reduces Recurrence and Death in Stage 3 dMMR Colon Cancer
A study in stage 3 dMMR colon cancer found that atezolizumab plus chemotherapy after surgery cut recurrence and death risk by 50%. The trial enrolled 712 patients and the regimen is now included in treatment guidelines.
A new treatment combining immunotherapy with chemotherapy after surgery cut the risk of cancer coming back and death by 50% for patients with a specific type of stage 3 colon cancer, according to research led by Mayo Clinic Comprehensive Cancer Center. The study focused on patients with stage 3 colon cancer who have a genetic makeup called deficient DNA mismatch repair, or dMMR. About 15% of people diagnosed with colon cancer have this type, and these tumors haven't responded well to chemotherapy alone.
Until now, chemotherapy after surgery has been the standard treatment for stage 3 colon cancer, but about 30% of patients still see their cancer return. The clinical trial enrolled 712 patients in the U.S. and Germany with dMMR stage 3 colon cancer that had been surgically removed and had spread to their lymph nodes. Half received chemotherapy for six months along with the immunotherapy drug atezolizumab, then continued the immunotherapy alone for another six months. The other half received chemotherapy alone.
The immunotherapy drug is an immune checkpoint inhibitor that reactivates the body's anti-tumor immunity to kill cancer cells. Researchers had previously found that tumors in patients with dMMR showed a large increase in immune cells that are targets of these inhibitors, which led them to test this treatment approach.
Based on the results, the combination of atezolizumab and chemotherapy is now the new standard treatment for stage 3 deficient mismatch repair colon cancer. The National Comprehensive Cancer Network has updated its guidelines to include this treatment recommendation. The guidelines also cover patients with high-risk stage 2 colon cancer where the tumor invades nearby structures but hasn't reached lymph nodes.
The study included patients with Lynch syndrome, the most common form of hereditary colon cancer, since these patients have tumors that show dMMR and are typically diagnosed younger. Colon cancer is the third most common cancer in the country, and more younger adults under 50 are being diagnosed with it. The study was presented at the 2025 American Society of Clinical Oncology Annual Meeting in Chicago and published in the New England Journal of Medicine.