Overcoming Resistance to Anti-EGFR Therapies: Mechanisms of Cetuximab and Panitumumab Resistance and Emerging Combination Strategies.

Cetuximab and panitumumab are anti-EGFR monoclonal antibodies widely used for the treatment of colorectal cancers.

However, due to various mechanisms of resistance to these targeted therapies, the patients' responses vary. These resistances remain a major obstacle in treatment and overcoming them has become a key emphasis of current therapeutic strategies. Intrinsic and acquired resistance often lead to reactivation of downstream signaling pathways, mainly the RAS-RAF-MEK-ERK (MAPK pathway) and PI3K-AKT axes. Prior existing mutations in KRAS, NRAS, and BRAF result in primary resistance by constantly activating the signals, irrespective of EGFR inhibition.

That said, acquired resistance manifests under therapeutic burden through the process of clonal evolution via KRAS and BRAF alterations, restoring MAPK pathway activity despite EGFR inhibition. In addition to those mutations, tumor cells exploit mechanisms independent of EGFR, such as the pathway bypass, which includes amplification of ERBB family receptors like HER2 (ERBB2) and activation of MET signaling. To overcome these resistances, novel strategies have emerged, which target multiple nodes within the oncogenic networks. Such methods include vertical pathway inhibition, multi-kinase inhibition, liquid-biopsy-guided therapy, and anti-EGFR rechallenge.

Reactivation driven by secondary mutation can be prevented by targeting multiple nodes within the MAPK cascade simultaneously, which is referred to as the vertical pathway inhibition. Overall, this review underscores that overcoming therapeutic resistance requires a multidimensional approach that integrates molecular profiling, rational combination therapies, and adaptive treatment. Finally, these advances underscore the shift toward precision oncology, where therapy is tailored to tumor evolution, leading to improved response and patient outcome.