Primary tumour side as a driver for treatment choice in RAS wild-type metastatic colorectal cancer patients: a systematic review and pooled analysis of randomised trials

Background Retrospective subgroup analyses of previous trials in the first-line therapy of RAS wt metastatic colorectal cancer (mCRC) suggested a predictive impact of primary tumour side on the efficacy of anti-epidermal growth factor receptor (EGFR) agents. Recently, new head-to-head trials of doublets/bevacizumab versus doublets/anti-EGFR, PARADIGM and CAIRO5 were presented. Patients and methods We searched for phase II and III trials comparing doublet chemotherapy plus an anti-EGFR or bevacizumab as the first-line treatment for RAS wt mCRC patients. Overall survival (OS), progression-free survival (PFS), overall response rate (ORR) and radical resection rate result in the overall study populations and, according to the primary side, were pooled together in a two-stage analysis with random effects and fixed effect models. The interaction between sidedness and treatment effect was then analysed. Results We identified five trials (PEAK, CALGB/SWOG 80405, FIRE-3, PARADIGM and CAIRO5), including 2739 patients, 77% left- and 23% right-sided. Among patients with left-sided mCRC, the use of anti-EGFRs was associated with higher ORR (74% versus 62%, OR = 1.77 [95% confidence interval {CI} 1.39–2.26–0.88], p < 0.0001), longer OS (hazard ratio [HR] = 0.77 [95% CI 0.68–0.88], p < 0.0001) and not significantly longer PFS (HR = 0.92, p = 0.19). Among patients with right-sided mCRC, the use of bevacizumab was associated with longer PFS (HR = 1.36 [95% CI 1.12–1.65], p = 0.002) and not significantly longer OS (HR = 1.17, p = 0.14). A subgroup analysis confirmed a significant interaction effect between the primary tumour side and treatment arm in terms of ORR (p = 0.02), PFS (p = 0.0004) and OS (p = 0.001). No differences in the radical resection rate were found according to treatment and sidedness. Conclusions Our updated metanalysis corroborates the role of the primary tumour location in the choice of the upfront therapy for RAS wt mCRC patients, leading to strongly recommend anti-EGFRs in left-sided tumours and to prefer bevacizumab in the right-sided.