Distinct MAPK and PI3K pathway mutations in different melanoma types in Taiwanese individuals.

Abstract

A number of studies investigating mutations of genes involved in MAPK and PI3K pathways in melanoma patients have been performed, most of which were based on Caucasian populations. We sought to identify BRAF, NRAS, MEK1, PI3K, and PTEN mutations and further determine possible correlations with clinicopathological parameters in Taiwanese patients with acral, non-chronic sun damaged (NCSD), or mucosal melanoma. Forty melanocytic nevi, 24 dysplastic nevi, and 175 melanomas from Taiwanese patients were analysed for mutations in BRAF, NRAS, MEK1, PI3K, and PTEN genes by PCR and direct sequencing. Immunohistochemical analysis of the respective proteins in nevi and melanomas were also performed to determine possible clinicopathological characteristics. In addition to the classic BRAFV600E mutation, a novel BRAFV600L mutation was identified in acral and sinonasal melanomas. A significantly reduced frequency of NRAS and BRAF mutations was noted compared with Caucasian-based studies. Increased immunohistochemical scores for pan-RAS and MEK1 and less nodal metastasis were associated with enhanced survival rates in acral and NCSD melanoma patients. Our findings suggest that oncogenic events may differ among melanomas in Asian patients geographically (e.g. between Japanese and Taiwanese patients). Moreover, distinct genetic alterations were noted among acral, NCSD, and mucosal melanoma patients in our study, and the expression of biomarkers correlated with clinical survival rates differentially among the various melanoma groups.