Another prospective cohort study by Kotsopoulos et al. observed a significantly lower cumulative incidence of breast cancer in BRCA1/2 mutation carriers who used ET compared to EPT after RRBSO after 10 years of follow-up, suggesting a possible adverse effect of progestin-based HRT (Kotsopoulos et al. 2018). The gene discussed is BRCA1; the disease is breast cancer.