MAP2K1 and melanoma: In vitro experiments confirmed tumor resistance to dabrafenib and trametinib, but not to ERK inhibition.14 MEK1T55IndelRT has also been reported to drive resistance in tumor xenografts.31 A meta-analysis by Johnson et al. described an overall incidence of 7% for MEK1/2 mutations in vemurafenib-resistant melanomas.32 Although frequently accompanied by atypical BRAFG593S, L597R, K601E mutations, BRAFV600E mutations or NRASQ61R mutations, MEK mutations are also found in primary melanomas in the absence of other driver mutations.3