Naturally occurring hormones (endogenous)
If you are post-menopausal, having increased concentrations of naturally occurring oestrogens or androgens is associated with higher breast cancer risk.
If you are pre-menopausal, having high levels of a hormone called ‘insulin-like growth factor’ is associated with a small increase in risk of breast cancer.
Consumed hormones (exogenous)
A small increase in risk exists while you are taking the oral contraceptive pill and in the ten years after stopping it. However, the underlying risk of breast cancer is low at the young ages when women typically use the pill.
If you are post-menopausal, taking combined hormone replacement therapy (HRT) for five or more years is associated with an increased risk of breast cancer. This risk is not evident for oestrogen-only forms of HRT. Click here to view Cancer Australia's position statement and recommendations on HRT and breast cancer risk.
Age at menopause
Women who experience menopause later (at age 55 or after) have twice the risk of developing breast cancer of women who experience natural menopause at ages younger than 45.
Age at puberty
Reaching puberty early prolongs the amount of time you are exposed to the fluctuating levels of oestrogen and other female hormones that are associated with the menstrual cycle. Starting menstruation before the age of 12 is associated with higher breast cancer risk.