LBA391^ Background: Efficacy and safety of first-line FOLFOX4 plus either cetuximab (weekly or every two weeks) have been reported to be similar in 152 patients with KRAS exon 2 wt mCRC within the randomized phase II CECOG/CORE2 study. Recent analyses have shown that also mutations in KRAS exons 3/4 and NRAS (exons 2, 3, and 4) are associated with an inferior PFS and OS with EGFR-targeted monoclonal antibody containing therapy. The impact of these additional mutations on the reported findings in the CECOG/CORE2 study were investigated. Methods: Tumor samples of 148 randomized KRAS exon 2 wild-type metastatic colorectal cancer patients were available for testing of additional mutations by conventional Sanger sequencing. Objective response rate (ORR), PFS and OS were compared in patients with KRAS (exons 2, 3, and 4) and NRAS (exons 2, 3, and 4) wild-type tumors [RAS wt] versus patients with mutations in KRAS (exons 3 and 4) or NRAS (exons 2, 3 and 4) [RAS mt]. Patients with BRAF mutations were excluded from this comparison. The Cochran-Mantel-Haenszel procedure was used to compare the ORR. Kaplan-Meier methods, log-rank test and Cox proportional hazard methods were used to analyze PFS and OS. Results: Of the 148 KRAS exon 2 wt patients 124 patients had RAS and BRAF wt tumors, 10 patients had RAS mutations only and 14 had only BRAF mutations. In the RAS wt and the RAS mt groups ORR was 61.3% (95% CI 52.1-69.9) and 40% (95%CI 12.2-73.8), (Odds ratio 0.43, p=0.1966). Median PFS was 9.7 months (95% CI 8.9-11.2) versus 7.2 months (95% CI 6.7-10.8) (hazard ratio HR=0.56, p=0.1135). Median OS was 28.5 months (95% CI 24.0-31.3) versus 16.3 months (95% CI 15.9-20.7), (HR=0.43, p=0.0199). The difference in OS remained statistically significant in the Cox model, if adjusted for significant confounding factors. ORR, PFS, and OS in BRAF mt and RAS mt patients were similar. Conclusions: RAS wt patients treated with cetuximab and FOLFOX4 experience a significant prolongation of OS as compared to RAS mt patients. This analysis supports the findings of other trials that RAS mutational analyses in metastatic CRC disease is recommended prior to initiation of an EGFR-targeted monoclonal antibody therapy. Clinical trial information: NCT00479752.
PULSE, a phase 2 study of mFOLFOX6-panitumumab (P) with biomarker stratification as first-line chemotherapy (CT), in patients (pts) with KRAS (exon 2) metastatic colorectal cancer (mCRC). A GEMCAD 09-03 study