WASHINGTON -- Women's health advocates expressed grave concern yesterday that a new study aimed at preventing breast cancer is failing to warn participants about the serious side effects of their drug therapy, including the possible development of blood clots and liver tumors.
Testimony about risks of the drug tamoxifen and inadequate warnings came as a congressional panel examined the first large-scale breast cancer prevention study, which was announced earlier this year by the National Cancer Institute.
Dr. Bernadine P. Healy, director of the National Institutes of Health, parent agency of the cancer institute, defended the projected five-year experiment involving 16,000 women aged 35 and older.
"We firmly believe there are more benefits than risks in the Breast Cancer Prevention Trial," Dr. Healy told the human resources and intergovernmental relations subcommittee of the House Government Operations Committee. She said the $68 million study "is well-grounded, well-designed and tightly monitored."
She was responding to a panel of cancer experts and some people familiar with the study who advised women to be cautious about participating.
Dr. Michael W. DeGregorio, professor of oncology at the University of Texas, said that stomach and liver tumors "may result from long-term use of tamoxifen" as envisioned in the study. He added that "many tamoxifen-related side effects are associated with chronic dosing for more than six months," including such lesser effects as hot flashes and menstrual irregularities.
Dr. Peter Greenwald, director of the cancer institute's prevention and control division, agreed that the study was controversial because it involved giving tamoxifen, a widely used cancer drug, to healthy women in order to prevent the disease. But he said that any side effects would be closely monitored.
More than 26,000 women have volunteered to take a daily dosage at 270 medical sites in the United States and Canada, and more than 3,000 have begun doing so.
Dr. Greenwald said that 16,000 women selected as having a high risk of breast cancer would be divided randomly into two groups, one of which will be given 20 milligrams of tamoxifen daily. The other group will take a placebo, a pill with no medical value.
Neither the women nor the physicians will know who is taking which pill, a process known as double-blinding, authorities said.
Breast cancer, which will afflict one in every nine women, will be ++ diagnosed in an estimated 180,000 women in the United States this year and cause 46,000 deaths, Dr. Greenwald said.
Dr. Healy said that new approaches at preventing cancer are crucial because "breast cancer is the leading cancer risk for women -- it is an epidemic." She said that tamoxifen has been prescribed for cancer patients for more than 20 years "and there is evidence that women at risk can benefit from this trial."
Dr. Healy added that the drug holds the promise of preventing 30 percent to 40 percent of breast cancer cases.
But Dr. Adriane Fugh-Berman, medical adviser to the National Women's Health Network of Washington, was among those who felt "the risks of tamoxifen have not been adequately described," including such side effects as dizziness, headaches, nausea and depression.
Women who run an above-average risk of incurring breast cancer, authorities said, are those over 60, women whose menstrual periods began early and women whose mothers, sisters or daughters have had the disease.