WASHINGTON — Tamoxifen, the first drug touted as a powerful preventive against breast cancer, won a reluctant nod Wednesday from government scientists advising the Food and Drug Administration.
But in recommending that the federal agency approve tamoxifen's use for preventing breast cancer in high-risk women, an FDA advisory panel expressed concern that the drug may do less--and for fewer women--than originally hoped.
Last April, researchers announced that tamoxifen appeared to cut the incidence of breast cancer by 45% in women taking it in a nationwide experiment. Cancer specialists across the nation hailed the first evidence of a drug that promised cancer prevention, not just treatment.
But the advisory panel cautioned Wednesday that tamoxifen may forestall the appearance of breast cancer for no more than five years, the maximum length of time that any woman should take it. And they added that because tamoxifen significantly increases a woman's risk of developing blood clots and uterine cancer, only those who are most likely to get breast cancer should take the drug as a preventive measure.
Also on Wednesday, an FDA advisory panel recommended approval of Herceptin, developed by California-based Genentech, as a treatment for advanced breast cancer--the first in a wave of promising gene-based cancer treatments.
Tamoxifen already is widely available as a treatment in patients who have developed breast cancer. At issue is whether the FDA should give its blessing to doctors who prescribe tamoxifen, produced by the British firm Zeneca Inc., for prevention. In making that decision later this year, the FDA is expected to rely heavily on Wednesday's recommendation by the advisory panel.
While the scientific panel saw potential benefits to allowing such labeling, it also dampened hopes that the drug could safely be used by large numbers of women to block cancer indefinitely.
"As yet, there is no compelling evidence for prevention," said Richard Schilsky of the University of Chicago Medical Center. "There is compelling evidence for reduction of short-term incidence of breast cancer."
The panel also warned that when a woman taking tamoxifen nevertheless develops breast cancer, it is unknown whether her cancer would be more virulent or more drug-resistant than it might have been had she not been taking the drug.
The panel said Zeneca must take steps to aggressively educate doctors to the risks of taking tamoxifen so that only women at very high risk are prescribed the drug. The study that first suggested tamoxifen's cancer-preventing properties also detailed its risky side effects: Women taking tamoxifen for three years were twice as likely as those not taking the drug to develop uterine cancer. And they were three times as likely to develop potentially fatal blood clots in the lungs.
Among both critics and proponents of tamoxifen there was agreement on two facts: First, that if the FDA allows Zeneca to label tamoxifen as a cancer-prevention drug, it will be far more widely prescribed than it is today. And second, that the FDA's decision in this case could establish the standards by which future cancer-prevention drugs will be judged.
"We're dealing with a preventive measure, which is pretty new," said Susan Braun, president of the Susan B. Komen Breast Cancer Foundation, who welcomed the advisory board's recommendation. "It's a healthy population initially. So the caution is really important."
But others saw a dark side.
"Drugs for prevention are used in healthy people and should be held to a higher standard than drugs used for life-threatening conditions," said Cynthia Pearson, executive director of the National Women's Health Network.
* BREAST CANCER DRUG: Genentech wins approval from an FDA panel for Herceptin. D1