GRB2 and neoplasm: The rationale for using PET/CT imaging with 18F-FDG in this tumor model was based on the overexpression of Igf2 and deletion of Wt1. Mutational inactivation of WT1 tumor suppressor also leads to activation of the IGF-1R signaling and its downstream targets such as Grb2 which signals through Ras, Raf, and ultimately mitogen-activated protein kinase (MAPK), which is involved in cellular events such as growth, differentiation, and stress response [40].