Limited and conflicting evidence exists regarding the risks associated with the use of HRT: (1) for oral and vaginal applications; (2) in the ER- and/or PR-positive breast cancer populations; and (3) for different durations of treatment (Brewster et al., 2007; Durna et al., 2002; Fahlen et al., 2013; Holmberg et al., 2008). This evidence concerns the gene PGR and breast cancer.