DEEPER Trial- Cetuximab + mFOLFOXIRI Shows Long-Term Signal in Left-Sided RAS/BRAF Wild-Type mCRC: JCO | September 2026

Introduction:

For RAS wild-type, left-sided metastatic colorectal cancer (mCRC), chemotherapy plus anti-EGFR therapy is an established first-line strategy. Whether intensifying the chemotherapy backbone to mFOLFOXIRI adds meaningful long-term benefit when combined with cetuximab remains uncertain. The final DEEPER analysis provides 5-year follow-up comparing mFOLFOXIRI plus cetuximab with mFOLFOXIRI plus bevacizumab.

Why was this study needed?

The original DEEPER trial demonstrated greater depth of response (DpR) with cetuximab.

Survival was longer than anticipated, making the original follow-up insufficient for mature OS assessment.

The clinically most relevant population is increasingly defined by both molecular status and primary tumor sidedness.

The extended analysis therefore focused particularly on RAS/BRAF wild-type, left-sided mCRC.

Results:

In the overall per-protocol population, there was no significant difference in PFS or OS between treatment groups.

However, among patients with RAS/BRAF wild-type, left-sided tumors:

Median PFS: 14.8 vs 11.9 months

HR 0.71 (95% CI 0.52–0.97); P=0.029

Median OS: 50.2 vs 40.2 months

HR 0.74 (95% CI 0.53–1.05)

Thus, the cetuximab strategy produced an approximately 10-month numerical improvement in median OS, although the confidence interval crossed 1.

Exploratory analyses suggested greater OS benefit with cetuximab in:

Men: HR 0.59; P=0.016

Patients with extrahepatic disease: HR 0.60; P=0.014

Clinical Impact:

The findings reinforce the importance of molecular selection + tumor sidedness when choosing biologic therapy in first-line mCRC.

For appropriately selected patients:

Left-sided + RAS/BRAF WT + need for major tumor shrinkage → intensive chemotherapy + anti-EGFR therapy may be particularly attractive.

The results also strengthen the concept that depth of response may carry longer-term clinical relevance, particularly when substantial tumor reduction could facilitate conversion strategies or improve subsequent treatment opportunities.

Caution:

DEEPER was a randomized phase II trial designed primarily around depth of response—not powered for definitive OS superiority.

The overall study population showed no significant survival advantage, and the key RAS/BRAF wild-type, left-sided analysis was a subgroup analysis. The OS HR of 0.74 had a 95% CI of 0.53–1.05, so superiority for OS cannot be claimed.

The apparent benefits according to sex and extrahepatic disease were exploratory and not adjusted for multiple comparisons and should therefore be considered hypothesis-generating.

Bottom Line:

In RAS/BRAF wild-type, left-sided mCRC, mFOLFOXIRI + cetuximab produced deeper tumor shrinkage and longer PFS than mFOLFOXIRI + bevacizumab, with median OS of 50.2 versus 40.2 months. The long-term signal is compelling but not definitive—supporting intensive anti-EGFR therapy as a selected strategy rather than establishing a universal new standard.