Hormone replacement therapy and the risk of breast cancer

Hormone replacement therapy (HRT) has had a chequered history ever since its initial use to manage menopausal symptoms. It is clear that it has many other effects and here we review its impact on the risk of breast cancer. A clear risk is seen for current uses of combined oestrogen/progestagen pills, but this returns to normal shortly after treatment cessation. The role of oestrogen only replacement therapy is less clear, but most studies find a weaker, but still positive, association in current users. Recent sharp reductions in HRT use have been correlated with declines in breast cancer incidence in the USA, but not so clearly elsewhere.