IGFBP5 and breast cancer: Further analyses based on these GWAS findings have identified several genes that might interact with MHT use on breast cancer risk, including SNPs regulating the fibroblast growth factor receptor two (FGFR2) gene20, as well as SNPs close to the Kruppel like factor 4 (KLF4) gene and the insulin like growth-factor-binding protein 5 (IGFBP5) gene21–23.