Mechanisms of Innate and Acquired Resistance to Anti-EGFR Therapy: A Review of Current Knowledge with a Focus on Rechallenge Therapies.

Abstract

Innate and acquired resistance to anti-EGFR therapy (EGFRi) is a major limitation in the treatment of metastatic colorectal cancer (mCRC). Although <i>RAS</i> genes are the most commonly mutated innate and acquired oncogenes in cancer, there are a number of other mechanisms that limit the effectiveness of EGFRi. Patients with innate resistance have been found to contain <i>BRAFV600E</i> mutations, and possibly <i>MET, MEK, PIK3CA, PTEN</i>, and <i>HER2</i> alterations. Meanwhile, <i>BRAFV600E</i> mutations may also be involved in acquired resistance to EGFRi, in addition to EGFR ectodomain mutations, <i>MET</i> alterations, and possibly <i>HER2</i> amplification. In addition, paracrine effects and cell-fate mechanisms of resistance are being increasingly described as contributing to acquired resistance. Utilization of circulating tumor DNA has been paramount in monitoring the dynamic nature of acquired resistance and has helped to guide treatment decisions, particularly in the EGFRi rechallenge setting. Herein, we provide an in-depth review of EGFRi-resistance mechanisms and describe the current therapeutic landscape in the hopes of identifying effective rechallenge strategies.