MAPK3 and glioblastoma: Only 1–3% of patients harbour the BRAF V600E mutation, but it is more frequent in children and young adults and in epithelial-type glioblastoma.114–117 Mutated BRAF causes constitutive activation of BRAF, leading to continued activation of its downstream effector MAPKs, MEK1/2 and ERK1/2.