BRAF — a tumour-agnostic drug target with lineage-specific dependencies

Abstract

In June 2022, the FDA granted Accelerated Approval to the BRAF inhibitor dabrafenib in combination with the MEK inhibitor trametinib for the treatment of adult and paediatric patients (≥6 years of age) with unresectable or metastatic BRAFV600E-mutant solid tumours, except for BRAFV600E-mutant colorectal cancers. The histology-agnostic approval of dabrafenib plus trametinib marks the culmination of two decades of research into the landscape of BRAF mutations in human cancers, the biochemical mechanisms underlying BRAF-mediated tumorigenesis, and the clinical development of selective RAF and MEK inhibitors. Although the majority of patients with BRAFV600E-mutant tumours derive clinical benefit from BRAF inhibitor-based combinations, resistance to treatment develops in most. In this Review, we describe the biochemical basis for oncogenic BRAF-induced activation of MAPK signalling and pan-cancer and lineage-specific mechanisms of intrinsic, adaptive and acquired resistance to BRAF inhibitors. We also discuss novel RAF inhibitors and drug combinations designed to delay the emergence of treatment resistance and/or expand the population of patients with BRAF-mutant cancers who benefit from molecularly targeted therapies. Various BRAF alterations are found and function as oncogenic drivers across diverse cancer types. BRAF inhibitor-based therapy has improved outcomes for patients with cancers harbouring BRAFV600 mutations, although resistance develops in most, and the current inhibitors are not effective against other types of BRAF alterations. In this Review, the authors describe the mechanisms underlying oncogenic BRAF signalling, as well as pan-cancer and lineage-specific mechanisms of intrinsic, adaptive and acquired resistance to BRAF inhibitors. They also discuss novel RAF inhibitors and drug combinations designed to overcome these resistance mechanisms and/or expand the applicability of molecularly targeted therapy to a broader range of BRAF-mutant cancers.