Location of primary tumor and benefit from anti-epidermal growth factorreceptor monoclonalantibodies in patients with RAS and BRAF wild-typemetastatic colorectal cancer

Introduction. Right- and left-sided colorectal cancers (CRCs) differ in clinical and molecular characteristics. Some retrospective analyses suggested that patients with right-sided tumors derive less benefit from anti-epidermal growth factor receptor (EGFR) antibodies; however, molecular selection in those studies was not extensive. Patients and Methods. Patients with RAS and BRAF wild-type metastatic CRC (mCRC) who were treated with single-agent anti-EGFRs or with cetuximab-irinotecan (if refractory to previous irinotecan) were included in the study. Differences in outcome between patients with right- and left-sided tumors were investigated. Results. Of 75 patients, 14 and 61 had right- and left-sided tumors, respectively. None of the right-sided tumors responded according to RECIST, compared with 24 left-sided tumors (overall response rate: 0% vs. 41%; p 5 .0032), and only 2 patients with right-sided tumors (15%) versus 47 patients with left-sided tumors (80%) achieved disease control (p, .0001). The median duration of progression-free survival was 2.3 and 6.6 months in patients with right-sided and left-sided tumors, respectively (hazard ratio: 3.97;95%confidence interval: 2.09–7.53; p,.0001). Conclusion. Patients with right-sided RAS and BRAF wild-type mCRC seemed to derive no benefit from single-agent anti- EGFRs.