New U.S. government numbers give some of the strongest evidence yet that menopause hormones can raise the risk of breast cancer.

Rates of the disease levelled off in 2004 after plunging in 2003, the year after millions of women stopped taking hormones because a big study tied them to higher heart, stroke and breast-cancer risks.

From 2001 to 2004, breast cancer rates fell almost nine per cent — a dramatic decline, researchers report in Thursday's New England Journal of Medicine.

The trend was even stronger for the most common form of the disease, tumours whose growth depends on hormones. Those cases fell almost 15 per cent among women aged 50 to 69, the group most likely to have been on hormone pills.

"The story has gotten stronger," said Dr. Peter Ravdin, a biostatistician at the University of Texas M.D. Anderson Cancer Center in Houston who led the research.

Some were skeptical when, several months ago, Ravdin and National Cancer Institute researchers first reported the 2003 drop and tied it to hormone use.

The new numbers, which add 2004, prove this was no fluke, said Dr. Julie Gralow, a spokeswoman for the American Society of Clinical Oncology and a cancer expert at the University of Washington in Seattle, who had no role in the study.

Hormone replacement therapy advice stands

For consumers, the new research does not change the advice to use the lowest dose of hormone replacement therapy for the shortest time possible for hot flashes and other menopause symptoms that cannot be controlled in any other way. Labels on hormones say they should not be used to try to prevent heart disease.

Although some recent analyses suggest the heart risks are not as great as had been believed for younger, newly menopausal women, the statistics out this week add to the worries about cancer.

After rising steadily through the 1990s, the U.S. breast cancer rate dipped from 2001 to 2002, from 138 cases to 135 cases per 100,000 women.

After the federal Women's Health Initiative study reported in July 2002 on the health risks of hormones, use of the pills plunged.

So did the breast cancer rate the following year — to 126 cases per 100,000 women. It was the steepest fall since the government started keeping records in the 1970s.

Cancers stopped?

The drop was seen in all of the registries that contribute cancer statistics to the government, and no big change was seen in any other type of cancer — strong signs that hormones were playing a role, specialists said.

The 2004 rate held steady at about 126 cases per 100,000.

Stopping hormone use may have stopped some cancers from growing and caused them to disappear, scientists speculate. Or it may have just slowed them down and they will progress and appear years later than they otherwise would have, said Ahmedin Jemal, an American Cancer Society researcher. Only time will tell which is true, he said.

Wyeth Pharmaceuticals, which makes top-selling hormone pills Prempro and Premarin, criticized the study. Company spokesman Dr. Joseph Camardo said hormone prescriptions continued to fall in 2004 but breast cancer rates did not decline proportionately.

Ravdin said the company's criticism does not invalidate the cancer trends.  More information should emerge later this year, when researchers are due to report followup data on participants in the Women's Health Initiative who went off hormone pills after the risks became known.

Last week, the Canadian Cancer Society said overall death rates and incidence rates for most cancers stabilized or declined over the last 10 years. Although an estimated 22,300 Canadian women will be diagnosed with breast cancer this year, the rate of new cases in women over age 40 seems to be stabilizing or dropping, the report said.