Efficacy of FOLFIRI plus bevacizumab versus FOLFIRI plus cetuximab in RAS-mutant metastatic colorectal cancer: Final update on patients with RAS-mutant metastatic colorectal cancer treated in FIRE-3.

3550 Background: Doublet chemotherapy plus bevacizumab is a well-established standard of care in the first-line treatment of RAS-mutant (RASmut) metastatic colorectal cancer (mCRC). The FIRE-3 trial was the first randomized study to compare FOLFIRI plus cetuximab to FOLFIRI plus bevacizumab in mCRC. Since this trial initially included patients irrespective of RAS mutation status, the present analysis performs an updated evaluation of therapeutic efficacy of targeted therapy with bevacizumab versus cetuximab in RASmut mCRC. Methods: FIRE-3 trial included 752 patients. Initially, pyrosequencing (PSeq) was used to identify RAS mutations. In a subsequent investigation next-generation sequencing (NGS) was applied in 373 available tumors. A 5% mutant allele cutoff was used for both PSeq and NGS both of which were done centrally. Results: Of the 224 RASmut and BRAF wild-type patients, 187 were identified by polymerase chain reaction (PCR) and PSeq, 122 by NGS. 86 tumors were PCR positive and NGS positive (PCR+/NGS+), 36 tumors PCR negative and NGS positive (PCR-/NGS+). In the overall RASmut cohort of 224 patients, no overall survival (OS) benefit was observed when cetuximab was compared to bevacizumab (20.3 months vs 21.1 months; HR 1.028; 95% CI, 0.547-1.583; P=.842). This effect was observed independent of sidedness of primary tumors (PT) for left-sided (21.5 months vs 22.1 months; HR 1.054; 95% CI, 0.763-1.456) and right-sided PT (19.2 months vs 19.5 months; HR 0.931; 95% CI, 0.547-1.583). Conclusions: While cetuximab notably is not effective in RASmut mCRC, this randomized comparison does not provide an indication for superior efficacy of bevacizumab in the first-line treatment of this patient group. Trial identification number: NCT00433927 clinicaltrials.gov