An update on the effects of MHT containing Estrogen alone or estrogen plus a progestogen on breast cancer risk

Professor Rodney Baber AM

 The University of Sydney

An association between Menopausal Hormone Therapy (MHT) use and increased breast cancer risk has been known for many years. Observational studies at the turn of the century together with RCT data from The Women’s Health Initiative trials subsequently showed a difference in the relative risk of breast cancer for estrogen only MHT compared to estrogen plus progestogen MHT. Long term follow-up of WHI data in 2020 showed estrogen only MHT was associated with a reduced risk of breast cancer and death from breast cancer whilst estrogen plus a synthetic progestin was associated with an increased risk of contracting breast cancer although risk of death was not increased.

Initially thought to be a class effect, subsequent observational studies found different relative risks of breast cancer for MHT containing different progestogens. These findings have been supported by recent observational data, predominantly from the UK which suggests a small increased risk of breast cancer with long term estrogen only MHT and a greater relative risk of breast cancer for MHT containing estrogen with various synthetic progestins. Combined MHT using estrogen with a neutral progestogen such as micronized progesterone or dydrogesterone was associated with minimal or no increased risk of breast cancer in these studies. Possible mechanisms to discuss these findings will be discussed.


Rod Baber is Clinical Professor of Obstetrics and Gynaecology at The University of Sydney and is Head of the Menopause and Menstrual disorders clinic at Royal North Shore Hospital.He is a Past President of The International Menopause Society and The Australasian Menopause Society and currently Editor in Chief of Climacteric, the journal of The International Menopause Society and an associate editor of The Australian and New Zealand Journal of Obstetrics and Gynaecology.

His awards include membership of The Order of Australia for services to Obstetrics and Gynaecology in clinical medicine and research and The RANZCOG Distinguished Service medal.