PRIME trial

Background

Phase III randomized trial in 1183 patients with previously untreated metastatic colorectal cancer. Compared first-line FOLFOX4 plus panitumumab versus FOLFOX4 alone; this report is the final analysis incorporating extended RAS (KRAS/NRAS) testing.

Interventions and follow up

Arm A: FOLFOX4 plus panitumumab 6 mg/kg every 2 weeks
Arm B: FOLFOX4 every 2 weeks
Primary endpoint: Progression-free survival (PFS)
Follow-up: Final analysis with extended RAS subgroups

Results

Median PFS, KRAS exon 2 wild-type: 10.0 mo vs 8.6 mo, arm A vs arm B (HR 0.80, 95% CI 0.67-0.95, P=.01)
Median PFS, KRAS exon 2 mutant: 7.4 mo vs 9.2 mo (HR 1.27, 95% CI 1.04-1.55, P=.02) — favors chemo alone
Median OS, RAS wild-type (final): 25.8 mo vs 20.2 mo (HR 0.77, 95% CI 0.64-0.94, P=.009)

Adverse events

Dermatologic: Any-grade skin toxicity 37% vs 2% (KRAS wt arm A vs B); 31% vs 1% (KRAS mt)
Electrolyte/GI: Hypomagnesemia 7% vs <1%, hypokalemia 10% vs 5%, mucositis 9% vs <1%, diarrhea higher with panitumumab
Hematologic: Neutropenia 37% vs 48% (KRAS mt arms), comparable across groups

Conclusions

Panitumumab plus FOLFOX4 significantly improved PFS and OS versus FOLFOX4 alone in RAS wild-type mCRC, while harming outcomes in RAS-mutant patients, confirming extended RAS testing as essential before anti-EGFR therapy.

Key Limitations

Extended RAS analysis was retrospective (though prespecified-updated); a proportion of samples were not evaluable for all RAS loci. Open-label design. Sidedness not a stratification factor in the original design.

Clinical Context

PRIME's extended-RAS analysis was pivotal in restricting anti-EGFR therapy to RAS wild-type tumors; FDA/EMA labels for panitumumab require RAS wild-type status. ESMO guidelines recommend panitumumab plus chemotherapy as a preferred first-line option for RAS wild-type, left-sided mCRC.

References