HRT and breast cancer

Research on hormone replacement therapy (HRT) in the 21st century has been dominated by the findings of the Women’s Health Initiative (WHI) and Million Women Study (MWS). Clinical practice has changed accordingly. Both studies confirm an increase in the risk of breast cancer among women using combined HRT (oestrogen and progestogen) when compared with women who have never used HRT. The risk among women using oestrogen-only preparations of HRT, according to the MWS, is increased, but to a lesser extent than for women using combined HRT. In contrast the WHI Study suggests that oestrogen alone is not associated with an increased risk of breast cancer. Despite these different findings most evidence-based guidelines from professional organizations still advise use of HRT only for the relief of menopausal symptoms and only short term. Routine use of unopposed oestrogen for women with a uterus is being discussed but is still not recommended. New data have also led to the recommendation that HRT is contraindicated for women who have had breast cancer. More research is needed on the contribution of progestogens to the increased risk of breast cancer and on the safety of different routes of administration of both oestrogen and progestogen.