For instance, IGF-1R binds IGF-1 with high affinity and has lower affinity to IGF-2 and insulin (Fig. 1), but IR-A has a higher affinity for insulin and IGF-2 and not for IGF-I.50 Additional data indicate IGF-1R/IR hybrid receptors have higher affinity to IGF-151; thus, this affinity for multiple receptors may allow IGF-1 to be tumorigenic in many types of cancer. This evidence concerns the gene INSR and cancer.