Breast cancer is the commonest cancer among women in the western world, accounting for up to 30% of all cancers in women. There is a long-standing controversy about the potential link to hormone replacement therapy (HRT), with large observational studies suggesting that HRT increases the risk, while the Women’s Health Initiative (WHI), a prospective, randomised placebo-controlled trial has reported several times over a period of 20 years that combined (oestrogen and progestogen) HRT increases the risk, while oestrogen-only HRT given to women who have had a prior hysterectomy, is associated with a significantly reduced risk of developing breast cancer.