Cetuximab versus bevacizumab in metastatic colorectal cancer: a comparative effectiveness study

Purpose Uncertainty exists regarding comparative effectiveness of cetuximab versus bevacizumab in metastatic colorectal cancer (mCRC). We conducted a retrospective head-to-head multi-cohort study comparing clinical outcomes from both antibodies Methods Cohorts were defined by treatment line and subgroups by (K)RAS status and tumour sidedness. Among other outcomes, we estimated and compared response rates, progression-free (PFS) and overall survival (OS). Results Between January 2010 and April 2018, 311 patients were included. Except for (K)RAS mutation status, baseline characteristics were balanced across treatment groups. In the full analysis of first and second-line cohorts, PFS (first-line: HR = 0.85; 95% CI 0.64 to 1.13; P = 0.26; second-line: HR = 1.16; 95% CI 0.74 to 1.83; P = 0.51) and OS (first-line: HR = 0.83; 95% CI 0.61 to 1.15; P = 0.26; second-line: HR = 0.88; 95% CI 0.56 to 1.38; P = 0.58) were similar between bevacizumab and cetuximab arms. In subgroup analyses of first-line therapy, we found a survival difference favouring bevacizumab in right-sided tumours (PFS: HR = 0.52; 95% CI 0.29 to 0.93; P = 0.025; OS: HR = 0.60; 95% CI 0.32 to 1.12; P = 0.11), but not in left-sided (HR = 1.04; 95% CI 0.75 to 1.46; P = 0.81; OS: HR = 0.94; 95% CI 0.65 to 1.36; P = 0.74), or (K)RAS wild-type tumours (PFS: HR = 0.91; 95% CI 0.60 to 1.40; P = 0.67; OS: HR = 0.79; 95% CI 0.50 to 1.25; P = 0.31). Response rates were similar across treatment groups, except for the subgroup of patients bearing right-sided primaries, where bevacizumab performed substantially better. Conclusion This study provides evidence suggesting bevacizumab and cetuximab lead to similar effectiveness outcomes in mCRC, except for right-sided tumours, where cetuximab seemed to show considerably poorer outcomes. Further research is needed to confirm these results.