MMTV‐ErbB2/neu mice represent OR‐negative/HER2‐positive disease and present with solid DCIS lesions that progress to invasive disease after 12–14 weeks, whereas MMTV‐iFGFR1 transgenic mice present with multicellular mammary epithelium with small collapsed lumens 2 weeks after FGFR1 induction and invasive progression at 4 weeks after FGFR1 induction.16, 17. Here, ERBB2 is linked to ductal breast carcinoma in situ.