When reports linked a remarkable decline in nationwide breast-cancer cases to falling numbers of women taking menopausal hormones, skeptics said it could just be that it was actually a drop in mammograms that meant fewer cancers were being detected.
Not so, says a large national study released Tuesday.
Researchers from Seattle and three other locations across the country say that their study of breast-cancer rates among more than 200,000 women – all of whom received regular mammograms – showed cancer rates fell significantly after U.S. women began abandoning menopausal hormone therapy about seven years ago.
The findings are to be published in today's Journal of the National Cancer Institute.
The study is the first to include only women who were regularly screened with mammography, thus reducing the possibility that a drop in cancer rates could be the result of fewer screenings.
It also adds to a growing body of evidence against hormone therapy.
"If you take away the hormones, your risk of breast cancer goes down," said Dr. Karla Kerlikowske, a physician at the San Francisco VA Medical Center and lead author of the study.
The study analyzed more than 600,000 mammography exams done on 232,000 women ages 50 to 69 between 1997 and 2003.
The women – from Washington, California, Vermont and New Hampshire – were part of the Breast Cancer Surveillance Consortium sponsored by the U.S. National Cancer Institute. Out of the group, 3,238 women were diagnosed with breast cancer within a year of a screening.
The study found a decrease in breast-cancer cases that coincided with the decline in women taking hormone pills to treat menopausal symptoms such as hot flashes, vaginal dryness and night sweats.
In 2000, menopausal hormone therapy began falling out of favor upon mounting evidence that it was dangerous.
Then in 2002, the landmark Women's Health Initiative study revealed that women who took Prempro, an estrogen-progestin pill, were more likely to develop breast cancer or to have a heart attack or strokes. Between 2002 and 2003, the number of Americans on hormone therapy plummeted 34 percent.
Tuesday's study also buttresses previous findings that women who are weaned off hormone therapy might be able to largely undo the risks within two or three years, Kerlikowske said.
Most notably, incidents of estrogen receptor-positive breast cancer – the type of tumor linked to estrogen-progestin therapy – fell by 13 percent each year from 2001 to 2003.
Half of the women in the study did not take hormones. The rest were taking or previously took estrogen-only or estrogen-progestin pills. Researchers did not break out the cancer data by type of therapy.
Not the end of hormones
The latest study, especially with its large sample size, should be one more argument underlining the risks of hormone therapy, said Dr. Julie Gralow, a breast oncologist with the Seattle Cancer Care Alliance and an associate professor at the University of Washington School of Medicine.
Nonetheless, "it doesn't mean that nobody should be on hormone-replacement therapy," she said.
Women who suffer from severe menopausal symptoms, for instance, still can benefit from hormone therapy if the drugs are given in low doses for short periods, Gralow said.
Diana Buist, one of the study's co-authors and a scientific investigator at Seattle's Group Health Center for Health Studies, said breast-cancer rates among the women in the study could continue to fall or even climb again, reflecting the complexity of determining exactly what drives cancer rates up or down.
And Buist cautions that women who quit taking hormone pills shouldn't also quit getting mammograms, particularly as they get older.
A woman born in the U.S. today still has a 12.7 percent chance of developing breast cancer in her lifetime, according to the National Cancer Institute.
And women now in their 60s are nearly three times more likely to get breast cancer than women in their 40s, the institute said.