However, one group has shown that while MEK1/2 inhibitors decreased levels of phosphorylated-ERK1/2 in GBM, regardless of NF1 status, growth inhibition occurred only in neurofibromin 1 (NF1)-deficient cells39, a protein that is frequently mutated in the Mesenchymal subtype40. Here, MAP2K1 is linked to glioblastoma.