IRS4 and breast cancer: To further substantiate the oncogenic capacity of Irs4, we derived a stable epithelial cell line (designated P3724-R4) from an MMTV-induced K14Cre;Trp53F/F mammary tumour from our insertional mutagenesis screen, with a known proviral integration in the Irs4 locus and a consequently high Irs4 expression.