A prospective study of 872 BRCA1 PV carriers of whom 43% (77% premenopausal, 23% postmenopausal at RRSO, mean age 43 years, range 30–70 years) took HRT for a mean of 3.9 years (range 0.5–19 years) concluded that estrogen alone did not increase breast cancer risk but the safety of progestin-containing HRT was uncertain.25 A 2019 systematic review including seven studies (n = 933 BRCA1/2 PV carriers) concluded that HRT could be used for up to 4.3 years without increasing breast cancer risk.26 Age at initiation of HRT may be important. This evidence concerns the gene BRCA1 and breast carcinoma.