HRT and breast cancer risk: what the evidence says

Breast cancer is common, and risk rises with age. HRT does not cause most cases, and many cases occur in women who have never used it. The question is whether HRT adds to baseline risk and by how much. Large observational studies and randomised trials have examined this, and guidance bodies have summarised them. The picture is nuanced, and research continues.

Oestrogen-only HRT is used by women who have had a hysterectomy. The NICE menopause guideline says that it is associated with little or no change in breast cancer risk. Some studies even suggested a lower risk in specific trials, but results are mixed and the safest statement is that any change is small. Taking oestrogen-only HRT does not remove the need for normal breast awareness and screening.

Combined HRT, which includes a progestogen, is associated with a small increase in breast cancer risk. The size depends on the type of progestogen, how long HRT is used and individual factors. The risk appears to be higher with longer use and to decline after stopping. NICE advises that women should be told about this when considering HRT. Evidence is not strong enough to say definitively whether micronised progesterone carries the same risk as synthetic progestogens, though some studies suggest it may be lower.

• Alcohol, excess weight and low physical activity are all linked to breast cancer risk, and the increase from combined HRT is of a similar order to some of these.

• HRT also has benefits, including relief of symptoms and bone protection, that need to be weighed against risks.

• Absolute risk depends on your age and baseline risk. A clinician can discuss figures relevant to you.

• Screening and breast awareness remain important whether or not you take HRT.

A family history of breast cancer does not automatically rule out HRT, but needs careful discussion. If you have had breast cancer, systemic HRT is generally not recommended without specialist advice, and non-hormonal options and vaginal oestrogen are considered with your oncology team. Women carrying BRCA gene variants have particular considerations, especially after risk-reducing surgery, and specialist guidance applies.

NICE advises review at three months and then yearly, discussing benefit, risk and whether to continue. There is no fixed time limit for using HRT, and many women use it for as long as benefit outweighs risk. Some choose to stop after a number of years. Both decisions are legitimate, and a clinician can help weigh them.