RAF-independent MEK mutations drive refractory histiocytic neoplasms but respond to ERK inhibition

-mutant patients with ulixertinib on prospective protocols, four of whom were refractory to MEK inhibition. Four of five patients experienced objective responses to ulixertinib. These data reveal the impact of oncogenic MEK mutations in vivo, identify patients with likelihood of resistance to MEK inhibition, and nominate ERK inhibition to overcome resistance to MEK inhibition in histiocytoses.