Dividing and conquering: controlling advanced melanoma by targeting oncogene-defined subsets

For decades, therapy for advanced melanoma has lagged behind most of the cancer field owing to its intrinsic resistance to conventional cytotoxic chemotherapy and limited impact of cytokine-based immunotherapy. The opportunity to develop molecularly targeted therapy emerged with the discovery of activating mutations in BRAF, a component of the long studied MAP kinase pathway. These mutations are found in approximately 50 % of patients with regionally advanced or metastatic melanoma and appear to be one of the initiating steps in the development of primary melanoma. Additional oncogenic events, particularly those that affect tumor suppressor genes, are essential for development of invasive and metastatic melanoma. Nonetheless, mutated BRAF retains its central contribution to melanoma pathophysiology even in advanced stage disease as manifested by the remarkable antitumor effects and alteration the natural history of metastatic melanoma of selective BRAF inhibitors. After initial response, resistance commonly emerges within a few months' time and the field has focused on delineating molecular mechanisms of resistance toward the goal of improving upon the early therapeutic effects of single agent BRAF inhibition. Combination regimens are currently undergoing clinical investigation. NRAS and CKIT mutant melanoma represent the next oncogene defined melanoma subsets for which initial targeted therapy approaches are being explored, with early evidence suggesting progress with MEK and CKIT inhibitors, respectively. A considerable subset of patients have melanomas that are not defined by the presence of BRAF, NRAS, or CKIT mutations and, thus, the elucidation of the entire melanoma genome is being pursued with the hope of identifying additional therapeutic targets.