MAPK3 and gastrointestinal stromal tumor: In GISTs, ERK1/2 inhibition reduced mTORC1 phosphorylation and decreased the inhibitory phosphorylation of GSK3β (Figure S7), indicating that MAPK/ERK pathway also regulates mTORC1 and GSK3β in KIT‐mutant GIST cells via ERK1/2 kinase (ERK).