The MWS reported that, compared to never users, the use of various types of oestrogen-progestagen combined HRT was associated with a higher risk of breast cancer (RR = 2.00, 95%CI 1.88 – 2.12) than use of oestrogens alone (RR = 1.30, 95%CI 1.21 – 1.40) or use of tibolone (RR=1.45, 95%CI 1.25 – 1.68).