WASHINGTON -- Thousands of healthy women taking part in a new large-scale trial to see if a potent drug can prevent breast cancer are being inadequately informed of the risks, the critics asserted at a congressional hearing.
Opponents of the $60 million federal study, designed to see if daily doses of the drug, tamoxifen, can prevent breast cancer in women with greater than normal risk of developing the disease, said yesterday the government had not informed participants of recent research that cast doubts on the drug's safety.
In addition, they said, centers enrolling women in the five-year trial are placing far more emphasis on unproven, possible benefits of the treatment than on side effects and potential risks.
Some centers have modified consent forms women must sign to participate so that they exclude or de-emphasize certain risks, critics said.
Officials of the National Institutes of Health defended the study, calling it one of the most important trials ever undertaken on female health.
The vast majority of information indicates that the drug is relatively safe to give to healthy women, and several outside panels of experts approved the study before it began, they said.
"We do not enter into clinical trials lightly," Dr. Bernadine Healy, the NIH director, told the House Government Operations Subcommittee on Human Resources and Intergovernmental Relations. "The most effective treatment for breast cancer is the prevention of breast cancer."
Dr. Healy noted that doctors were already prescribing tamoxifen to women at risk of breast cancer because of early indications that it might stave off the disease. The only way to see if the drug works as a preventive, or ends up being unacceptable because of adverse effects, is to do a controlled trial, she said.
"There are things we don't know about tamoxifen, that's the reason for the trial," Dr. Healy testified. Experts from the National Cancer Institute, the NIH unit that is sponsoring the trial, said previous research indicated that tamoxifen could reduce the number of expected breast cancers by at least one-third.
Dr. Adriane Fugh-Berman, representing the National Women's Health Network, said the not-for-profit advocacy group remained opposed to the study, which would give tamoxifen to 8,000 healthy women over age 35 while another 8,000 in the control group receives placebo pills.
"The women eligible for enrollment are not truly at high risk for breast cancer and tamoxifen is too toxic for use in healthy women," Dr. Fugh-Berman said. "While the benefits of tamoxifen for primary prevention are highly questionable, the risks are well-documented."
Tamoxifen is a synthetic hormone that was discovered 30 years ago and has been in clinical use for more than 15 years.
The drug competes with the female hormone estrogen and blocks its effects, and has proven particularly useful against tumors that depend upon estrogen to grow.