BRAF and melanoma: Non-V600 BRAF mutations, including K601E, have been associated with sensitivity to MEK inhibition.25,26 The G466R and N581S BRAF mutations were found in melanomas that also harboured mutant NRAS. As activating BRAF and NRAS mutations are considered mutually exclusive,4 these two BRAF mutations are probably non-activating, or may be low-activity BRAF mutants that require upstream RAS activation.