This hybrid receptor (IGF-1/IR) is made from the linkage of the αβ subunits, encoded by both the InsR and IGF-1R genes, into a heterodimeric receptor.37 Isoforms of both receptors exist, but the most important isoform to cancer biology is the insulin receptor-alpha (IR-A), which is also the fetal form of IR. This evidence concerns the gene IGF1 and cancer.