Stage III colon cancer: US approves immunotherapy after surgery for the first time

On 8 October 2026, the US Food and Drug Administration (FDA) approved Roche's drug atezolizumab (brand name Tecentriq) for a new use: as adjuvant treatment after surgery for stage III colon cancer. It is given together with chemotherapy consisting of a fluoropyrimidine and oxaliplatin. The approval applies only to tumours with deficient mismatch repair (dMMR) – a trait in which the cancer cells' repair system is impaired and particularly many mutations accumulate. According to Roche, such tumours have the potential to respond to immunotherapy; they are identified with an immunohistochemistry test.

The decision is based on the phase III ATOMIC trial involving 712 patients, published in the New England Journal of Medicine. Half received twelve cycles of chemotherapy (mFOLFOX6) plus atezolizumab followed by around six months of atezolizumab alone, the other half chemotherapy only. According to Roche, the risk of recurrence or death fell by 50 percent; the FDA gives the hazard ratio as 0.50. According to Roche, 86 percent of patients on the combination were free of recurrence after three years, compared with 76 percent in the control group. The manufacturer said the safety profile was consistent with previous studies; the FDA lists immune-mediated adverse reactions and infusion reactions among its warnings.

According to Roche, around 15 percent of colon cancer patients have tumours with dMMR or high microsatellite instability (MSI-H). Almost one in four colon cancers is diagnosed at stage III, and nearly 30 percent of these patients relapse within five years. For now, the approval applies only in the US; Roche plans to file with the European Medicines Agency (EMA), among others, but gave no timeline. Whether the therapy is suitable in an individual case can only be judged by the treating oncologists.