NRAS and melanoma: Our data are consistent with findings that endogenous DUSP4 levels vary between melanoma cell lines in vitro.51 Relative overexpression of DUSP4 and ETV4 in SK-MEL-23 compared with CHL-1 may reflect the fact that SK-MEL-23 cells harbour amplified wild-type BRAF.52 Both cell lines used in this study harbour wild-type NRAS; given that ~60% of patients in the clinical DOC-MEK study had NRAS mutant melanoma, it may be informative to assess the contribution of DUSP4 and ETV4 to MEK inhibitor response in NRAS mutant cell lines.