ESR1 and breast cancer: Curiously, expression of some ER-inducible gene markers, such as progesterone receptor (PR), pS2, Bcl2 and cathepsin D, does not show any significant relationship with the age at diagnosis [13,18], while other markers show increased expression in breast cancers arising earlier in life [20] – suggesting that the effects of aging may in part be attributed to age-related differences in estrogen-inducible ER pathways.