In this sense, our results indirectly signify that HRT may potentially increase the already elevated risk of breast cancer in BRCA1 carriers who have a history of cancer, even when estrogen alone may be safe relative to estrogen plus progesterone (12% vs. 22% 10-year incidence of breast cancer) in BRCA1 carriers who never had cancer. This evidence concerns the gene BRCA1 and breast carcinoma.