Among 31 patients with BRAF–mutant melanomas treated with either the BRAFi, PLX4032/vemurafenib or GSK2118436/dabrafenib, 5 MEK1 exon 3 mutations (P124S in 4, I111S in 1) were detected in baseline melanoma tumors of 5 distinct patients...Four of 5 patients with BRAF/MEK1 double-mutant baseline melanomas displayed objective responses in the tumors biopsied, and 3 of 5 patients achieved overall partial response...