Menopausal hormone treatment and breast cancer

Breast cancer risk is a central concern in shared decision-making when considering menopausal hormone treatment (MHT). Women spend approximately 40% of their lives in menopause, and climacteric symptoms can substantially impair quality of life. MHT is the most effective strategy to treat climacteric symptoms. MHT can consist of the administration of oestrogen only in women who have undergone hysterectomy or a combined treatment of oestrogen and progestogen in women with a uterus. The risk of breast cancer associated with MHT varies with both the individual's baseline risk of breast cancer and the type of treatment. Oestrogen only therapy in women who have undergone hysterectomy appears associated with a lower risk of breast cancer than combined oestrogen and progestogen MHT. Micronised progesterone and dydrogesterone seem associated with a lower risk of breast cancer than progestins, as shown in observational or case-control studies, but no randomised study has addressed this questions. Evaluating baseline risk of breast cancer before prescription of MHT should be considered a minimum standard alongside education on risk factors that can help decrease the risk of breast cancer with or without using MHT. This Review synthesises contemporary randomised and observational evidence, including pharmacologic distinctions, interaction with modifiable risk factors, and implications for better shared decision-making for women considering MHT.