Should Anti-EGFR Agents Be Used in Right-Sided RAS Wild-type Advanced Colorectal Cancer?

Purpose of Review Colorectal cancer is the third most common cancer worldwide with a high mortality rate at the advanced stages of the disease. Treatment options are dependent on the stage of the disease, patients’ performance status, and the specific molecular makeup of the tumor. Adding an anti-epidermal growth factor receptor monoclonal antibody (anti-EGFR mAb) to conventional chemotherapy in molecularly selected patients (i.e., RAS wild-type) leads to a survival advantage. We aim to review the latest evidence on the influence of primary tumor location (PTL) on treatment response to chemotherapy combined with an anti-EGFR in patients with metastatic colorectal cancer (mCRC). Recent Findings Colon cancer arising on the left side versus the right side of the colon portrays different outcomes, emerging PTL as an important characteristic in understanding the outcomes for patients with colorectal cancer. Patients with right-sided tumors have a worse prognosis than those with left-sided tumors. Primary tumor location may also be predictive of treatment benefit from targeted therapy with an anti-EGFR or anti-VEGF in the treatment of RAS wild-type mCRC. Although no benefit in overall survival (OS) has been demonstrated, available data up to now can endorse the use of an anti-EGFR in right-sided RAS wild-type advanced colorectal cancer if the therapy goal is tumor shrinkage (given the higher objective response rate). However, the majority of data on PTL has been obtained through retrospective analysis of clinical trials where PTL was neither part of the stratification nor pre-planned subgroup analysis, rendering it susceptible to recall bias. Summary There is a great necessity to improve our understanding of the molecular and histological variability in left versus right-sided colon cancer and its impact on future targeted therapy.