MAP2K1 mutations were first identified in HCL‐variant [6], a distinct disease that has a worse prognosis than classic HCL [7], and in a patient with relapsed HCL‐variant harboring mutant MAP2K1 (K57N) treatment with the MEK inhibitor trametinib was only modestly active (stable disease after 6 cycles) [8]. The gene discussed is MAP2K1; the disease is hairy cell leukemia.