Breast cancer

The risk of breast cancer varies depending on a person's modifiable and non-modifiable risk factors, such as being overweight, drinking alcohol or increasing age. For more information on risk factors for breast cancer, see NICE CKS guidance.

OESTROGEN ONLY HRT

NICE says:

• Oestrogen only HRT slightly increases the risk of breast cancer compared to not taking HRT and the increase rises with longer duration of use, is greater in current users compared to past users, declines after stopping HRT but persists for at least 10 years after stopping use.
• There is no difference in breast cancer risk between transdermal and oral oestrogen.

COMBINED HRT

NICE says:

• Combined HRT increases the risk of breast cancer compared with not taking HRT, and the increase rises with duration of use.
• The increase is higher in current users compared to past users.
• The increase declines after stopping HRT, but persists at least 10 years after stopping use.
• Sequential combined HRT preparations increase the risk of breast cancer less than continuous combined HRT preparations.
• It is not known with certainty whether preparations containing micronised progesterone or dydrogesterone have a different increased risk for breast cancer compared with preparations containing other progestogens, due to limited data.

The BMS says:

• Any increase in breast cancer risk is small and estimated at less than 0.1% per annum or an incidence of <1.0 per 1000 women per year of use.
• Results from the E3N Cohort study, a large observational French study, suggest that oestrogens combined with micronised progesterone or dydrogesterone do not increase breast cancer risk for up to 5 years of use and after this there is a small increased risk.

It must be emphasised that findings from the E3N cohort study are based on observational data and, for this reason, any conclusions remain tentative.

VAGINAL OESTROGEN

• Studies suggest low-dose vaginal oestrogens preparations do not increase the risk of breast cancer.

POI PATIENTS AND EARLY MENOPAUSE

• The BMS says HRT is unlikely to increase risk of breast cancer in women with POI.
• Regarding early menopause, the most recent update from NICE states that evidence shows an increased risk of breast cancer for people with early menopause who used HRT compared to those not using HRT.