BRAF gene copy number and mutant allele frequency correlate with time to progression in metastatic melanoma patients treated with MAPK inhibitors

Metastatic melanoma is characterized by complex genomic alterations, including a high rate of mutations in driver genes and widespread deletions and amplifications encompassing various chromosome regions. Among them, chromosome 7 is frequently gained in BRAF-mutant melanoma, inducing a mutant allele–specific imbalance. Although BRAF amplification is a known mechanism of acquired resistance to therapy with MAPK inhibitors, it is still unclear if BRAF copy-number variation and BRAF mutant allele imbalance at baseline can be associated with response to treatment. In this study, we used a multimodal approach to assess BRAF copy number and mutant allele frequency in pretreatment melanoma samples from 46 patients who received MAPK inhibitor–based therapy, and we analyzed the association with progression-free survival. We found that 65% patients displayed BRAF gains, often supported by chromosome 7 polysomy. In addition, we observed that 64% patients had a balanced BRAF-mutant/wild-type allele ratio, whereas 14% and 23% patients had low and high BRAF mutant allele frequency, respectively. Notably, a significantly higher risk of progression was observed in patients with a diploid BRAF status versus those with BRAF gains [HR, 2.86; 95% confidence interval (CI), 1.29–6.35; P ¼ 0.01] and in patients with low percentage versus those with a balanced BRAF mutant allele percentage (HR, 4.54; 95% CI, 1.33–15.53; P ¼ 0.016). Our data suggest that quantitative analysis of the BRAF gene could be useful to select the melanoma patients who are most likely to benefit from therapy with MAPK inhibitors.