Adding atezolizumab cut the risk of stage III dMMR colon cancer returning

On October 8, 2026, the FDA approved atezolizumab, given with a fluoropyrimidine and oxaliplatin, as additional treatment after surgery for adults and children 2 and older with stage III mismatch-repair-deficient colon cancer. The same review also approved a subcutaneous form, atezolizumab with hyaluronidase, for patients 12 and older who weigh at least 40 kilograms. A dose for younger or lighter children has not been set.

The evidence is the ATOMIC trial, NCT02912559. It enrolled 711 adults and one child whose stage III dMMR tumors had been fully removed, with no remaining lymph-node disease and no metastases. They were randomly assigned to atezolizumab plus mFOLFOX6 for 12 cycles, then atezolizumab alone for six months, or to mFOLFOX6 alone for 12 cycles. The main result was disease-free survival. The hazard ratio was 0.50, with a 95 percent confidence interval of 0.35 to 0.73, so the risk of the cancer returning or of death was about half on the atezolizumab arm. Median disease-free survival was not reached in either group, which means the trial has not produced a median time. Overall survival was not the result the FDA cited. The label warns about immune-mediated side effects, infusion reactions, complications if a patient later has a donor stem-cell transplant, and harm in pregnancy. The approval is for this adjuvant use. It is not a statement that the cancer is gone.