Effect of KRAS and NRAS mutations on treatment outcomes in patients with metastatic colorectal cancer (mCRC) treated first-line with cetuximab plus FOLFOX4: New results from the OPUS study.

LBA444 Background: Patients with KRAS exon 2 codon 12/13 wild-type (wt) mCRC benefit significantly from the addition of cetuximab to first-line FOLFOX4 in relation to response and progression-free survival. Patients with KRAS exon 2 codon 12/13 mutations show no benefit with a trend to worse clinical outcomes. Methods: Tumors from OPUS study patients previously defined as KRAS codon 12/13 wt (n=179) were screened for specific mutations in KRAS exons 3 and 4 (8) and NRAS exons 2, 3, and 4 (18) using BEAMing technology. Treatment outcomes were assessed according to mutation status. Results: RAS tumor mutation status was evaluable for 118/179 (66%) patients. Mutations at the screened loci were detected in 36 (31%) patients. In the RAS wt population, there was benefit associated with the addition of cetuximab to FOLFOX4 (Table). In the overall RAS-mutant population, there was less favorable clinical outcome and no benefit from the addition of cetuximab to FOLFOX4. Conclusions: Patients with mCRC harboring any...