Immunotherapy Enhances Chemotherapy Effectiveness in Stage 3 Colon Cancer Treatment

Recent research conducted by the Mayo Clinic Comprehensive Cancer Center has demonstrated that combining immunotherapy with traditional chemotherapy after surgical removal significantly improves treatment outcomes for patients with stage 3 colon cancer, particularly those with a specific genetic profile known as deficient DNA mismatch repair (dMMR). This advancement offers promising new approaches to combat a cancer type that, despite being the third most common in the U.S., has seen relatively slow progress in treatment innovations.

Colon cancer remains a major health concern, with early detection through screening aiding in prevention and control. However, treatments such as chemotherapy have not been entirely effective, especially since approximately 30% of patients experience recurrence despite standard therapy. The recent multi-center trial, presented at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting, enrolled 712 patients with surgically removed tumor cells in lymph nodes. These patients had dMMR tumors, a genetic characteristic present in about 15% of colon cancer cases, which traditionally showed less responsiveness to chemotherapy.

The study tested the addition of an immune checkpoint inhibitor called atezolizumab—designed to activate the immune system to target and eliminate cancer cells—to the usual six months of chemotherapy, followed by a further six months of immunotherapy alone. Results revealed that this combination reduced cancer recurrence and mortality by approximately 50%, marking a substantial breakthrough in treatment for this subgroup.

Dr. Frank Sinicrope, the study lead, emphasized the significance of these findings, stating that this new treatment paradigm could rewrite standard care practices for stage 3 dMMR colon cancer. Historically, surgery followed by chemotherapy was the norm, yet recurrence remained a challenge. This innovative approach leverages the understanding that dMMR tumors tend to provoke an inflammatory immune response, making them more vulnerable to immune-targeted therapies.

The research not only benefits patients with sporadic cases but also includes those with Lynch syndrome, the most common hereditary form of colon cancer characterized by dMMR tumors. Moving forward, the research team plans to collaborate with the National Comprehensive Cancer Network to establish this promising immunotherapy-chemotherapy combination as the new standard of care for stage 3 deficient mismatch repair colon cancer.

This development underscores the importance of integrating personalized, genetics-based approaches into cancer treatment protocols, offering hope for better survival rates and quality of life for patients facing this challenging diagnosis.