Mutation stability in primary and metastatic melanoma: what we know and what we don't.

Despite the efficacy and success of targeted therapies, a significant number of patients with melanoma exhibit either intrinsic or acquired resistance to these drugs. Numerous mechanisms for the development of resistance have been postulated, but the precise reason for this is not known. In this review, we examine the incidence of mutations in select genes (BRAF, NRAS, C-KIT, and GNAQ) known to occur in melanoma, specifically in primary tumors and their paired metastases, to understand the significance of intratumoral heterogeneity by assessing how changes in mutation status alters the process of metastatic spread. Our data revealed a small yet consistent degree of discordance of mutations in the MAPK pathway commonly occurring in melanoma indicating that failed targeted therapy may be a consequence of this.