BRAF and MEK Inhibitors: Use and Resistance in BRAF-Mutated Cancers.

The mitogen activated protein kinase/extracellular signal-related kinase (MAPK/ERK) signaling pathway serves an integral role in growth, proliferation, differentiation, migration, and survival of all mammalian cells. Aberrant signaling of this pathway is often observed in several types of hematologic and solid malignancies. The most frequent insult to this signaling cascade, leading to its constitutive activation, is to the serine/threonine kinase rapidly accelerating fibrosarcoma (RAF). Considering this, the development and approval of various small-molecule inhibitors targeting the MAPK/ERK pathway has become a mainstay of treatment as either mono- or combination therapy in these cancers. Although effective initially, a major clinical barrier with these inhibitors is the relapse of patients due to drug resistance. Knowledge of the mechanisms of resistance to these drugs is still premature, highlighting the need for a more in-depth understanding of how patients become insensitive to these pharmacologic interventions. Herein, we will succinctly summarize the milestones in the approval of select MAPK/ERK pathway inhibitors, their use in patients, and major modes of resistance.