Targeting BRAF in melanoma: Biological and clinical challenges

Melanoma is an aggressive form of skin cancer that causes the greatest number of skin cancer-related deaths worldwide. In its early stages malignant melanoma can be cured by surgical resection, but once it has progressed to the metastatic stage it is extremely difficult to treat and does not respond to current therapies. A majority of cutaneous melanomas show activating mutations in the NRAS or BRAF proto-oncogenes, components of the Ras-Raf-Mek-Erk (MAPK) signal transduction pathway. The discovery of activating BRAF mutations in ∼50% of all melanomas has proved to be a turning point in the therapeutic management of the disseminated disease. This review summarizes the critical role of BRAF in melanoma pathophysiology, the clinical and pathological determinants of BRAF mutation status and finally addresses the current state of the art of BRAF inhibitors. We further outline the most recent findings on the mechanisms that underlie intrinsic and acquired BRAF inhibitor resistance and describe ongoing preclinical and clinical studies designed to delay or abrogate the onset of therapeutic escape.