FDA Approves Atezolizumab Plus Chemo for Stage III dMMR Colon Cancer

The FDA has approved atezolizumab (Tecentriq) in combination with a fluoropyrimidine and oxaliplatin for the adjuvant treatment of adult and pediatric patients 2 years of age and older with stage III mismatch repair–deficient colon cancer.¹

The regulatory agency also approved atezolizumab and hyaluronidase-tqjs (Tecentriq Hybreza; subcutaneous atezolizumab) in combination with a fluoropyrimidine and oxaliplatin for the adjuvant treatment of adult and pediatric patients 12 years of age and older who weigh 40 kg or greater with stage III dMMR colon cancer.

The approval was supported by data from the phase 3 ATOMIC/ML39057 trial (NCT02912559), in which atezolizumab plus chemotherapy improved disease-free survival (DFS) compared with mFOLFOX6 (oxaliplatin, leucovorin, and fluorouracil) alone (HR, 0.50; 95% CI: 0.35-0.73; P = 0.0001). The median DFS was not reached in both arms.

How was the ATOMIC trial conducted?

ATOMIC investigators enrolled patients at least 12 years of age with completely resected, histologically confirmed, stage III colon adenocarcinoma that was dMMR per local immunohistochemistry or site-selected reference laboratory, with central confirmation retrospectively conducted.² The study included patients with Lynch syndrome, and all patients needed to have an ECOG performance status of 0 to 2.

No prior chemotherapy or radiation was allowed, outside of a single cycle of mFOLFOX6 while awaiting dMMR test results.

Patients were randomly assigned 1:1 to receive atezolizumab plus mFOLFOX6, or mFOLFOX6 alone. In both arms, mFOLFOX6 was given for 12 cycles. In the experimental arm, patients received atezolizumab at 840 mg intravenously every 2 weeks for the first 12 cycles in combination with chemotherapy, followed by monotherapy for an additional 13 cycles.

DFS served as the primary end point. Secondary end points comprised overall survival (OS) and safety.

What additional efficacy data were reported from ATOMIC?

Findings also showed that at a median follow-up of 40.9 months (interquartile range [IQR] 26.7-58.6), the 3-year DFS rates were 86.3% (95% CI, 81.8%-89.8%) in the atezolizumab arm vs 76.2% (95% CI, 70.9%-80.6%) in the control arm.

OS outcomes were similar between the 2 arms. At a median follow-up of 45.8 months (IQR, 32.0-64.7), the 5-year OS rate was 89.7% (95% CI, 85.2%-92.9%) in the atezolizumab arm compared with 87.9% (95% CI, 83.1%- 91.4%) in the mFOLFOX6 group (stratified HR 0.90; 95% CI, 0.55-1.47; P =.68).

References

1. FDA approves atezolizumab in combination with chemotherapy for Stage III mismatch repair deficient colon cancer. FDA. October 8, 2026. Accessed October 8, 2026. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-atezolizumab-combination-chemotherapy-stage-iii-mismatch-repair-deficient-colon-cancer
2. Sinicrope FA, Ou FS, Arnold D, et al. Atezolizumab plus FOLFOX for stage III mismatch repair–deficient colon cancer. N Engl J Med. 2026;394(12):1155-1166. doi:10.1056/NEJMoa2507874