New research stirs debate over hormone replacement therapy

The number of post-menopausal women diagnosed with breast cancer in Canada fell markedly in the two years following a blockbuster study that revealed the dangers of hormone replacement therapy.

Research published in the U.S.-based Journal of the National Cancer Institute shows that, between 2002 and 2004, the breast cancer incidence rate fell 10 per cent among women aged 50 to 64. In that same time period, sales of HRT - drugs commonly used to alleviate the symptoms of menopause - fell by half.

"The research findings add to the international body of evidence that HRT use is linked to increased breast cancer risk," Dr. Prithwish De, an epidemiologist at the Canadian Cancer Society, said in an interview.

But Dr. Jennifer Blake, chief of obstetrics and gynecology at Sunnybrook Hospital in Toronto, took issue with that interpretation, saying that there are many other factors that could explain the declining number of cases of breast cancer among post-menopausal women.

"I don't know how they can suggest a drop of that magnitude can be linked solely to HRT," she said in an interview.

The U.S.-based Women's Health Initiative, published in 2002, found that women taking estrogen and progestin together had higher rates of breast cancer and heart disease, and those who took estrogen alone had a higher risk of stroke.

The study was a bombshell and provoked a fierce debate - the controversy about the safety and appropriate use of HRT rages on. That's because the WHI study also showed that the risk of breast cancer increases the longer a woman takes HRT, leading many experts to conclude that short-term use was safe. Others argued that there were many other plausible explanations for changes in breast cancer incidence such as different patterns of screening mammography and soaring obesity rates.

The new study is the first done using Canadian data. It shows that, in this country, mammography rates were unchanged in the 2002-2004 period.

Dr. De said this shows the drop in breast cancer incidence cannot be explained by fewer women getting mammograms. "The only factor that changed substantially was HRT use," he said.

While the new research focused on the two-year period after publication of the Women's Health Initiative study, it showed too that breast cancer incidences continued to decline gradually through to 2005 in women aged 50 to 69. It has increased slightly since then. (There was little change in breast cancer incidence rates in women under 50 and those over 70, researchers found.)

Dr. Blake said this is important, suggesting that the drop in breast cancer cases is a fluctuation, not due to a single change such as declining HRT use.

In 2002, nearly 30 per cent of Canadian women aged 50 to 69 were taking some form of hormone therapy. That number dropped to 15 per cent in 2004 and has remained fairly steady since.

In women of reproductive age, the ovaries produce two female hormones: estrogen and progesterone. With menopause, the ovaries stop producing these hormones and this can lead to symptoms such as hot flashes, night sweats, trouble sleeping, mood swings and vaginal dryness. Hormone therapy can be used to relieve these symptoms.

The Society of Obstetricians and Gynaecologists of Canada, in its guidelines, says that HRT is effective treatment for the symptoms of menopause and safe for periods of up to five years.

A three-month prescription for Premarin, the most-sold HRT in Canada, costs about $100.

Heather Chappell, director of cancer control policy at the Canadian Cancer Society, said the new research reaffirms the group's position that, generally speaking, the risks of HRT outweigh the benefits, and the drugs should be used only to treat severe symptoms of menopause and after consulting a physician. "The severity of each woman's menopausal symptoms and her medical history should be considered. If a woman decides to take HRT, she should take the lowest effective dose for the shortest time possible," she said.

In 2010, an estimated 23,200 Canadian women will be diagnosed with breast cancer and about 5,300 will die from the disease, according to the Canadian Cancer Society. More than 80 per cent of breast cancer cases occur in women aged 50 and older.