The government is launching the largest cancer prevention experiment in U.S. history today, testing 16,000 healthy women to see if the drug tamoxifen can prevent breast cancer.
If the experiment is successful, the estrogen-like drug could become an important tool in the fight against breast cancer, which struck 175,000 American women last year. Over a lifetime, one in nine American women will get breast cancer.
The new study also is exciting researchers in other fields because tamoxifen has been linked to lowered risk of heart attacks in women and to reduced risk of bone loss.
Tamoxifen, which is approved by the U.S. Food and Drug Administration, has been shown to be a good "adjuvant" therapy for warding off recurrence after breast cancer surgery. In women who have had cancer in one breast, it also can keep cancer from appearing in the other breast.
But with all the hope and promise, some women's health advocates are worried about the wisdom of giving such a powerful drug to healthy women, in part because it may increase the risk of uterine cancer and possibly liver cancer.
They also feel that, while the government describes the trial as a study of women "at increased risk" of breast cancer, it actually will include women whose only risk is being age 60 or more.
In simultaneous news conferences scheduled today in Boston, Bethesda, Md., and other cities included among the 270 sites for the trial, officials from the National Cancer Institute and leading specialists will spell out details.
Medical officials said women age 35 and older will be eligible for the five-year trial. Some 8,000 will be randomly chosen to receive 20 milligrams a day of tamoxifen, an estrogen-like drug that both mimics and blocks estrogen,
The other 8,000 will be assigned to receive placebos.
Tamoxifen is believed to retard cancer growth by blocking estrogen receptors in tumors that are driven by estrogen, a natural hormone.
While the government says the trial will involve "women at increased risk" for breast cancer, women's health advocates argue that many low risk women will be included, which could skew the results.