Atezolizumab + FOLFOX in Stage III CRC: NEJM| March 2026

Introduction

Stage III colon cancer is traditionally treated with adjuvant oxaliplatin-based chemotherapy such as FOLFOX. However, tumours with mismatch repair deficiency (dMMR) represent a biologically distinct subgroup with high immunogenicity and responsiveness to immune checkpoint inhibition in metastatic settings. Whether this immunotherapy benefit can be translated into the curative, adjuvant setting has remained a critical unanswered question. The ATOMIC trial addresses this gap by evaluating the addition of atezolizumab, a PD-L1 inhibitor, to standard mFOLFOX6 in resected stage III dMMR colon cancer.

Problem Statement

Despite standard adjuvant chemotherapy, recurrence rates in high-risk stage III colon cancer remain significant. dMMR tumours, although prognostically favourable in early stages, still demonstrate recurrence risk in stage III disease. The key clinical challenge has been whether incorporating immunotherapy early—before recurrence—can meaningfully improve disease-free survival and potentially cure rates.

Summary

In this phase III trial, adding atezolizumab to mFOLFOX6 significantly improved outcomes. At a median follow-up of 40.9 months, 3-year disease-free survival was 86.3% in the combination group compared to 76.2% with chemotherapy alone, translating to a 50% reduction in recurrence or death risk. This represents one of the first strong pieces of evidence supporting immunotherapy in the adjuvant setting for colon cancer. However, this benefit came with increased grade 3–4 adverse events (84.1% vs 71.9%), highlighting the need for careful patient selection.

Overall, this study marks a major step toward precision oncology in early-stage colon cancer, potentially redefining the standard of care for stage III dMMR disease.