Vemurafenib: targeted inhibition of mutated BRAF for treatment of advanced melanoma and its potential in other malignancies.

Vemurafenib is the first molecularly targeted therapy to be licensed in the US and Europe for treatment of advanced melanoma. Its mechanism of action involves selective inhibition of the mutated BRAF V600E kinase that leads to reduced signalling through the aberrant mitogen-activated protein kinase (MAPK) pathway. Its efficacy is restricted to melanomas carrying the BRAF V600E mutation, which is seen in approximately 50% of all melanomas. In a randomized phase III trial, it was superior to dacarbazine in first-line treatment of advanced melanoma, with an overall response rate (ORR) of 48% (95% CI 42, 45), an estimated 6-month progression-free survival (PFS) of 5.3 versus 1.6 months (hazard ratio [HR] 0.26; 95% CI 0.20, 0.33; p < 0.001) and a statistically superior 12-month overall survival (OS) rate of 55% versus 43% (HR 0.62 [95% CI 0.49, 0.77]). Vemurafenib is generally well tolerated, but its use can be associated with development of cutaneous neoplasms such as squamous cell carcinoma (SCC) and keratoacanthoma (KA). These lesions can be excised safely without the need for withholding the drug or reducing its dose. Mechanisms of resistance to vemurafenib do not involve development of secondary mutations in the BRAF kinase domain, but may be related to BRAF V600E over-amplification, bypassing mechanisms via upregulation and overexpression of other components in the MAPK signalling cascade or activation of alternative pathways with potential to enhance cell growth, proliferation and survival. Clinical trials to test the efficacy of vemurafenib in combination with immunomodulatory agents, such as ipilimumab, and MAPK kinase (MEK) inhibitors, such as GDC-0973, in the treatment of advanced melanoma are currently underway. Also under investigation is the use of vemurafenib in other solid tumours with BRAF mutations, such as papillary thyroid cancer.