• There is a very clear connection between hormone replacement therapy (HRT) and the risk of developing breast cancer.1,2 In the Million Women Study, current users of HRT at recruitment were more likely than never users to develop breast cancer (adjusted relative risk 1.66)3 Breast cancer risk increases the longer HRT is taken.1,2
  • Based on a comprehensive amount of evidence, the IARC has concluded that long-term combined estrogen-progestogen menopausal therapy causes cancers of the breast.4
  • The risk depends on the length of use of HRT and is reduced once treatment is stopped, levelling off 5 or more years after stopping treatment.5
  • Combined estrogen-progestogen oral contraceptives are associated with an increased risk of breast cancer, notably among young women.4
  • Women currently or recently taking oral contraceptives have a 15-25% higher risk of breast cancer compared with women who have never used oral contraceptives. This risk levels off 10 or more years after stopping oral contraceptive use.5

For women who do not have a history of breast cancer it is advisable to discuss the risks and benefits of taking HRT with your doctor in order to make an informed decision as to whether HRT is right for you. It is further recommended that you review your current treatments with your doctor on a regular basis to know if they are still your best option. If you opt for HRT, ask to take the lowest effective dose for the shortest amount of time needed to treat your symptoms.

HRT is generally not recommended if you have a history of breast cancer as HRT may increase your risk of a recurrence of breast cancer (see HABITS trial). Any decision to take HRT should, therefore, be discussed in detail with your physician.

  1. Women’s Health Initiative Study (
  2. Million Women Study (
  3. Million Women Study Collaborators. Breast cancer and hormone replacement therapy in the Million Women Study. Lancet 2003, 362: 419-27
  4. Stewart BW, Wild CP, editors (2014). World Cancer Report 2014. Lyon, France: International Agency for Research on Cancer
  5. Boyle, P., Levin, B. (eds.). World Health Organisation. International Agency for Research on Cancer. World Cancer Report 2008