Here's what you need to know about menopausal hormone therapy and cancer risk

The use of hormone replacement therapy (HRT) doubles the risk of breast cancer in menopausal Australian women, our new research shows.

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.

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.

Among women with breast cancer, menopausal hormone therapy increases the risk of the cancer coming back.

The good news is that the elevated risks of menopausal therapy generally wear off within a few years of ceasing use.

Risks and benefits of HRT

Hormone therapy is an effective treatment for menopausal hot flushes, night sweats, vaginal dryness and thinning of the vaginal tissues. These symptoms can have major effects on quality of life for women.

It’s less clear if menopausal hormone therapy alleviates other menopausal symptoms that aren’t as clearly related to hormone levels, such as irritability, low mood and mood swings.

Menopausal hormone therapy has also been shown to reduce the risk of hip fractures and, potentially, bowel cancer.

But in terms of the balance of potentially life-threatening disease with use of menopausal therapy, the number of cases of breast cancer, stroke, ovarian cancer, blood clots and endometrial cancer caused by therapy exceeds the number of hip fractures and bowel cancers prevented.

So, the risks of these serious diseases outweigh the benefits. And the risks of combined oestrogen-progestagen therapy are greater than those of oestrogen-only.

These risks and benefits underpin the regulators' recommendations for more than a decade in Australia, the United Kingdom and the United States that:

• Menopausal hormone therapy should only be used for the short-term treatment of menopausal symptoms (such as hot flushes, night sweats, vaginal dryness)

• Women considering using menopausal hormone therapy should be informed of its risks and benefits

• Menopausal hormone therapy shouldn’t be used to prevent disease, or (in Europe and Australia) as first-line treatment for osteoporosis

• HRT should be used for as short a period of time as possible and the need for continuing use should be reviewed every six to 12 months.

Preventing breast cancer

The publication of studies in 2002 and 2003 showing the risks of serious disease with HRT outweighed the benefits prompted immediate and rapid declines in use.

Menopausal hormone therapy use in Australia fell by 55% from 2001 to 2005. This was accompanied by a 9% fall in breast cancer diagnoses in women aged 50 and over, or around 800 fewer women diagnosed with invasive breast cancer annually. Similar reductions in use and subsequent breast cancer rates occurred in the United States.

The research published in the early 2000s attracted intense scrutiny. It was released at a time when menopausal therapy was widely used and promoted for its benefits, including the notion that it was “good” for women and would keep them healthier and somehow younger. Strong commercial interests were also at play.

Around 12% of women aged 40 to 65 years, or 500,000 women in Australia, are currently using menopausal hormone therapy. The majority have used it for more than five years.

Menopausal hormone therapy is estimated to cause at least 450 breast cancers each year in Australia – around 3.5% of all breast cancers.

More judicious and shorter-term use of menopausal hormone therapy could therefore further reduce the number of women suffering hormone therapy-related breast cancer, ovarian cancer and stroke.

What does this mean for you?

Menopausal hormone therapy should not be universal or automatic for women going through menopause. Nor should it be used to prevent diseases relating to ageing. This is a major change from what I was taught when I went to medical school in the early 1990s.

Although the news about the risks of hormone therapy isn’t great, it’s good that we’re aware of these risks and we no longer face the situation where many millions of women are using it, with little reliable evidence on its effects.

We now know that menopausal hormone therapy is a medication like any other, with risks and benefits and specific indications for use, including the treatment of moderate to severe menopausal symptoms, in informed women.

It’s not for doctors, researchers or other commentators to decide how to balance relief of menopausal symptoms against the risks of HRT for individual women considering use. That difficult task falls to women themselves, supported by the sum-total of the worldwide evidence and professionals and practice informed by that evidence.

When friends and family ask me about whether or not they should use menopausal hormone therapy, I advise that the current evidence is that they should avoid it if they can.

If they have menopausal symptoms that are sufficiently severe to warrant therapy, hormone therapy remains an important option. But it should be used for as short a time as possible, with regular (preferably six-monthly) reviews to check whether it’s still needed.

Emily Banks receives funding from the National Health and Medical Research Council, the Federal Department of Health and the Heart Foundation of Australia. She is currently Chair of the Advisory Committee on the Safety of Medicines; the views expressed in this article are her own.