IGF1 and neoplasm: In the case of IGF1, an IGF1 mutant in which the Arg residues at positions 36 and 37 to Glu mutant, R36E/R37E was defective in inducing IGF1R signaling and suppressed cell proliferation induced by WT IGF1 in vitro and tumor growth in vivo (dominant-negative antagonistic action)[11].