GRB2 and cancer: Upon binding of HGF to MET, the kinase domain phosphorylates growth factor receptor-bound protein 2 (GRB2) and GRB2-associated binding protein 1 (GAB1) and activates diverse downstream signaling pathways important in cancer, including the ERK/MAPK, PI3K-Akt/PKB, Crk-Rap, and Rac-Pak pathways [4].