Preexisting MEK1 exon 3 mutations in V600E/KBRAF melanomas do not confer resistance to BRAF inhibitors

As BRAF inhibitors gain widespread use for treatment of advanced melanoma, biomarkers for drug sensitivity or resistance are urgently needed. We identify here concurrent activating mutations in BRAF and MEK1 in melanomas and show that the presence of a downstream mutation in MEK1 does not necessarily make BRAF–mutant melanomas resistant to BRAF inhibitors.