Distinguishing clinicopathologic features of patients with V600E and V600K BRAF-mutant metastatic melanoma.

Abstract

Certain clinicopathologic features correlate with BRAF mutation status in melanoma including younger age and primary subtype. This study sought to determine the BRAF mutation status by age-decade and whether BRAF-mutant genotypes correlated with clinicopathologic features and outcome in patients with metastatic melanoma. A prospectively assembled cohort of Australian patients were followed from diagnosis of metastatic melanoma (N = 308). Clinicopathologic variables were correlated with BRAF mutational status, genotype, and survival. Forty-six percent of patients had a BRAF mutation; 73% V600E, 19% V600K, and 8% other genotypes. An inverse relationship existed between BRAF mutation prevalence and age-decade (P < 0.001). All patients <30 years and only 25% ≥ 70 years had BRAF-mutant melanoma. Amongst BRAF-mutant melanoma, the frequency of non-V600E genotypes (including V600K) increased with increasing age. Non-V600E genotypes comprised <20% in patients <50 years and >40% in those ≥ 70 years. A higher degree of cumulative sun-induced damage correlated with V600K but not V600E melanoma (P = 0.002). The disease-free interval from diagnosis of primary melanoma to first distant metastasis was shorter for patients with V600K compared with V600E melanoma (17.4 vs. 39.2 months, P = 0.048), with no difference in survival thereafter. In patients BRAF tested at diagnosis of metastatic melanoma, one year survival from diagnosis of metastasis was significantly longer for patients with BRAF-mutant melanoma treated with an inhibitor (83%), than those not treated with an inhibitor (29%, P < 0.001), or patients with BRAF wild-type melanoma (37%, P < 0.001). Different genotypes exist within BRAF-mutant metastatic melanoma, representing biologically and clinically discrete subtypes, suggesting distinct etiology and behavior.