The CRYSTAL and OPUS randomised clinical trials demonstrated that adding cetuximab to first-line chemotherapy in patients with KRAS wild-type metastatic colorectal cancer (mCRC) significantly improved treatment outcome compared with chemotherapy alone. The objective of this pooled analysis was to further investigate these findings in patients with KRAS wild-type tumours using extended survival data and following an enhancement in the ascertainment rate of KRAS and BRAF tumour mutation status from these studies.

Pooled individual patient data from each study were analysed for overall survival (OS), progression-free survival (PFS) and best overall response rate (ORR) in patients evaluable for KRAS and BRAF mutation status. Treatment arms were compared according to mutation status using log–rank and Cochran–Mantel–Haenszel tests.

In 845 patients with KRAS wild-type tumours adding cetuximab to chemotherapy led to a significant improvement in OS (hazard ratio [HR] 0.81; p=0.0062), PFS (HR 0.66; p<0.001) and ORR (odds ratio 2.16; p<0.0001). BRAF mutations were detected in 70/800 evaluable tumours. No significant differences were found in outcome between the treatment groups in these patients. Prognosis was worse in each treatment arm for patients with BRAF tumour mutations compared with those with BRAF wild-type tumours.

Analysis of pooled data from the CRYSTAL and OPUS studies confirms the consistency of the benefit obtained across all efficacy end-points from adding cetuximab to first-line chemotherapy in patients with KRAS wild-type mCRC. BRAF mutation does not appear to be a predictive biomarker in this setting, but is a marker of poor prognosis.