MAGGIE FOX

Reuters

January 14, 2008 at 6:24 PM EST

WASHINGTON — Hormone replacement therapy can raise the risk of an uncommon type of breast cancer fourfold after just three years, U.S. researchers reported on Monday.

They found women who took combined estrogen/progestin hormone-replacement therapy for three years or more had four times the usual risk of lobular breast cancer.

Their study, published in the January issue of Cancer Epidemiology, Biomarkers and Prevention, is one of dozens trying to paint a clearer picture of what dangers might come from taking HRT to treat menopause symptoms.

"Previous research indicated that five or more years of combined hormone-therapy use was necessary to increase overall breast-cancer risk," Dr. Christopher Li of the Fred Hutchinson Cancer Research Center, who led the study, said in a statement.

"Our study, the first specifically designed to evaluate the relationship between combined HRT and lobular breast cancers, suggests that a significantly shorter length of exposure to such hormones may confer an increased risk."

Lobular breast cancer accounts for about 10 per cent of invasive breast cancer -- the kind that threatens to spread -- according to the American Cancer Society.

It can be treated with hormone-based therapies such as tamoxifen, but the tumours are more difficult to detect by mammograms, meaning it is often diagnosed in more advanced stages.

Dr. Li's team asked more than 1,500 post-menopausal women in western Washington about whether they had used HRT. Of the women, 1,044 had breast cancer and 469 did not.

They found that women currently taking HRT were about three times as likely as other women to be among the cancer patients and those who used combined HRT for three or more years had a higher risk of lobular cancer.

They said that incidence of invasive lobular cancer rose by 52 per cent in the United States between 1987 and 1999 and that cases of ductal-lobular breast cancer rose by 96 per cent during that time.

Rates of ductal cancer rose 3 per cent over the same time.

"Our research suggests that the use of post-menopausal hormone-replacement therapy, specifically the use of combined estrogen-plus-progestin preparations, may be contributing to this increase," said Dr. Li.

For many years, doctors had thought hormone therapy could protect women from chronic diseases, especially heart disease.

But use of HRT plunged after the 2002 Women's Health Initiative study found that HRT could raise the risk not only of breast and ovarian cancer, but of strokes and other serious conditions.

Research since then shows the incidence of breast cancer dropped by 8.6 per cent between 2001 and 2004 in the United States -- along with the decline in HRT use.

Doctors stress that younger women who need the drugs to relieve serious symptoms of menopause should still consider taking them because new, lower-dose formulations are available and doctors now know to prescribe them for short periods of time.

"These findings are still of considerable public-health importance considering the estimated 57 million prescriptions for menopausal hormone therapy that continue to be filled in the United States," Dr. Li said.

• Reuters