The study, published in the International Journal of Cancer, is consistent with international research and demonstrates that more judicious use of hormonal therapy could reduce rates of breast cancer.
But that doesn’t mean HRT has no place in alleviating moderate to severe symptoms of menopause such as hot flushes and vaginal dryness.
Hormones and breast cancer.
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.
Breast cancer is also more common in women with higher oestrogen levels and can be reduced with oestrogen-blocking medications such as tamoxifen.
Our joint Cancer Council NSW-Australian National University study compared the use of menopausal hormone therapy in 1,236 women with recently diagnosed invasive breast cancer and 862 women without cancer.
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The findings are consistent with international evidence showing the risk of breast cancer increases the longer menopausal hormone therapy is used. The risks are greater with use of combined oestrogen-progestagen than with oestrogen-only therapy.
Current users of oestrogen-only therapy (who have been on HRT for around five years) have a 20% increase in the relative risk of developing breast cancer. Use for around ten years leads to a 30% increase in risk.
Corresponding figures for oestrogen-progestagen therapy are 60% (for five years of use) and 120% (for ten years).
The risks of breast cancer are increased, but to a lesser extent, with use for less than five years.
Breast cancer is relatively common. Among 1,000 women in their 50s, around ten would be expected to develop breast cancer over a five-year period. This would increase to 16 if those 1,000 women were taking oestogen-progestagen menopausal hormone therapy.