BRCA1 and breast cancer: However, HRT, particularly combined oestrogen and progesterone preparations, increases breast cancer risk and use is relatively contraindicated in women with or at high risk of breast cancer, although, paradoxically, recent observational data indicate that HRT use does not increase risk of breast cancer after BRRSPO in BRCA1 and possibly not BRCA2 carriers (Anderson et al, 2003; Collaborators MWS, 2003; Rebbeck et al, 2005).