Abstract 23: Low incidence of BRAFV600E mutation among melanoma patients in Ireland.

Abstract

Abstract Background: Aberrant activity of the mitogen-activated protein kinase (MAPK) signalling pathway represents a critical factor in the initiation and development of melanoma. Activation can be the result of largely mutually exclusive somatic mutations of KIT, NRAS, or more frequently, BRAF(V600E). The FDA and EMA approval of a BRAF inhibitor (vemurafenib) that blocks the function of the BRAFV600E protein established a new paradigm for targeted drug development. Currently, BRAF inhibitors are one of the most promising approaches to treat metastatic melanoma. Methods: In this study, we applied mass spectrometry-based SNP genotyping (Sequenom) to detect single nucleotide mutations in 33 cancer-related genes including BRAF, NRAS, KIT, CTNNB1, GNAS, and MET. PCR and extension primers for the multiplexed assay were designed with the Sequenom Assay Design software. Samples were processed as recommended by the manufacturer. Matrix chips were assayed on a Sequenom MassArray MALDI-TOF Mass Array system. Visual inspection and Sequenom Typer software were used to perform genotyping based on mass spectra. We compared two independent melanoma cohorts, one from Ireland (SVUH cohort; n=97) and the other from Belgium (Leuven cohort; n=60). Results: Intriguingly, patients from Ireland showed significant lower BRAFV600E mutation rates (19.0%) when compared to the mutation frequency seen with the Belgian cohort (43.3%) or with the mutation frequency reported by other studies on non-Irish populations (50-70%). In addition, BRAFV600K mutation is rare in the SVUH cohort (1.0%) compared with the Leuven cohort (6.7%). Mutations in BRAFV600M and V600R were <2% in both groups. Although the number of NRASQ61 mutant cases was slightly higher among the Irish melanoma patients compared with Belgium patients (20.6% and 13.3%, respectively), this does not fully account for the difference in BRAFV600E mutation rate. In contrast, many BRAFV600 WT patients in the SVUH cohort carried significantly increased mutation rates in MET (11.4%) compared to the Leuven cohort (0%) and reported elsewhere (2%). c-MET is a receptor tyrosine kinase that activates multiple signal transduction pathways, including MAPK, PI3K, WNT, and Notch. MET inhibitors that are currently in clinical trials include cabozantinib and foretinib and might be a valuable alternative treatment strategy for patients exhibiting this mutation. Mutation rates of the other examined genes were always <5% and did not significantly differ between the groups. Conclusion: Our observation of reduced BRAFV600E mutation rates in Irish patients will directly impact future treatment strategies for these patients. The identification of substantial mutation rates in MET opens up opportunities for targeting a significant subset of melanoma patients with MET inhibitors. Citation Format: Balazs Balint, Karin van den Hurk, Sinead Toomey, Louise Unwin, Kieran Sheahan, Enda McDermott, Ian Murphy, Joost van den Oord, Mairin Rafferty, Bryan Hennessy, William M. Gallagher. Low incidence of BRAFV600E mutation among melanoma patients in Ireland. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 23. doi:10.1158/1538-7445.AM2013-23