Understanding the risks of menopausal hormone therapy

By Emily Banks

Many women use menopausal hormone therapy (MHT, also known as HRT) but our new research has shown menopausal Australian women who are currently using MHT have double the risk of breast cancer compared to those who have never used it.

This is consistent with international evidence and demonstrates that more judicious use of hormonal therapy will reduce rates of breast cancer.

But that doesn't mean MHT has no place in alleviating moderate to severe symptoms of menopause.

Hormone levels have long been known to influence the development of breast cancer.

The reduction in hormone levels that occurs during menopause is protective; while the risk of breast cancer increases with age, it increases less steeply after menopause. Oestrogen blocking medications like tamoxifen also reduce risk.

Our joint ANU-Cancer Council NSW study, published in the International Journal of Cancer, compared the use of MHT in 1,236 women with recently diagnosed invasive breast cancer and 862 women without cancer.

The findings are consistent with international evidence showing the risk of breast cancer increases the longer MHT is used.

The risks are greater with use of combined oestrogen-progestogen than with oestrogen-only therapy.

The worldwide evidence shows current users of oestrogen-only therapy who have been on HRT for around five years have a 20 per cent increase in the relative risk of developing breast cancer.

Use for 10 years increases risk by 30 per cent.

Corresponding figures for oestrogen-progestogen therapy are 60 per cent (for five years of use) and 120 per cent (for 10 years).

Breast cancer is relatively common.

Among 1,000 women in their 50s, around 10 develop breast cancer over a five-year period.

This increases to 16 if they were taking oestrogen-progestogen MHT over a five-year period.

Among women with breast cancer, MHT increases the risk of the cancer coming back.