To avoid the compensatory mechanisms mediated by the IGFIR-IRs system, we used an IGFIR-KO BC model preferentially expressing IRA or IRB that we identified as MCF7KOIGF1R-IRA and MCF7KOIGF1R-IRB BC cells comparing the observed effects with cells expressing endogenous levels of IR named MCF7KOIGF1R-EV. This evidence concerns the gene IGF1R and breast cancer.