Effectiveness of first‐line cetuximab in wild‐type RAS metastatic colorectal cancer according to tumour BRAF mutation status from the EREBUS cohort

Aims Poor efficacy has been reported for patients with BRAF mutations for metastatic colorectal cancer (mCRC). Methods EREBUS is a French cohort study of wild‐type (wt) KRAS unresectable mCRC patients initiating a first‐line treatment with cetuximab from 2009 to 2010, followed for two years (five years for vital status). Molecular genetics platforms have provided additional RAS and BRAF mutation testing results. Progression‐free survival (PFS) and overall survival (OS) were assessed according to tumour mutation (mt) status: RASmt/BRAFany, RASwt/BRAFmt and RASwt/BRAFwt. Multivariate Cox analyses were used to evaluate association between mutation status and death or progression. Results A total of 389 patients were included in 65 centres and with a known tumour mutation status: 64 RASmt/BRAFany (21%), 33 RASwt/BRAFmt (13%) and 213 RASwt/BRAFwt (87%). Respective baseline characteristics were: median age 65, 64 and 63 years, male gender 63%, 64% and 69%, Eastern Cooperative Oncology Group performance status ≤ 1 75%, 76% and 79%, and liver‐only metastases 39%, 33% and 40%. Median progression‐free survival was 8.0 months [5.9–9.3] for patients with RASmt/BRAFany, 6.0 months [2.3–7.2] for patients with RASwt/BRAFmt, and 10.4 months [9.5–11.0] for patients with RASwt/BRAFwt. Respectively, median overall survival was 18.4 months [10.9–23.3], 9.7 months [6.9–16.6] and 29.3 months [26.3–36.1]. In multivariate analyses, progression (HR = 2.71 [1.79–4.10]) and death (HR = 2.79 [1.81–4.30]) were more likely for RASwt/BRAFmt vs RASwt/BRAFwt patients. Conclusions BRAF mutations were associated with markedly poorer outcomes in initially unresectable RASwt mCRC patients treated by cetuximab in first‐line treatment.