We then followed the mammary tumor development in older mice and found that 63% of the p16−/−;Brca1MGKO mice (n = 8) and 44% of p16+/−;Brca1MGKO mice (n = 9) developed mammary tumors at 11–20 months and 16–23 months, respectively (Table 1, and Supplementary Table S1), whereas no p16−/−, p16+/− or Brca1MGKO mice did so at similar ages (Table 1). Here, CDKN2A is linked to breast cancer.