Pioneering work from the Medina lab (Behbod et al. 2009), which was refined by the Brisken lab (Sflomos et al. 2016), showed that intraductal injection of ER+ breast cancer cells (i.e., into the mammary ducts of mice rather than the fat pad) could accurately recapitulate the metastatic process observed in women, with slow-growing tumours at endogenous estrogen levels, that would metastasise to the same four secondary organs seen in patients with ER+ breast cancer. This evidence concerns the gene ESR1 and breast cancer.