Although no parity history was available on these publicly available cases, upon applying our PPBC gene signature to this YWBC cohort (n = 311 patients with both ER+ and ER− disease) we observed a highly significant decrease in 15-year overall survival in breast cancer patients with a PPBC Hi signature score (HR 2.134, p = 0.0011) compared with those with a low score (PPBC Lo, Fig. 5f). This evidence concerns the gene ESR1 and breast cancer.