Final Results from the NSABP Breast Cancer Prevention Trial Reported
Scientists from the National Surgical Adjuvant Breast and Bowel Project (NSABP) who conducted the landmark Breast Cancer Prevention Trial (BCPT), report a seven-year and final update of the trial results in the November 16, 2005, Journal of the National Cancer Institute*. In this final report, reductions in breast cancer incidence among participants taking tamoxifen were found to be very similar compared to those reported in 1998 when initial findings from the BCPT were released. The conclusion is supported by the observation that the incidence rate of breast cancer was relatively constant through seven years of follow-up among women who received tamoxifen and by the fact that the rate remained stable for at least two years beyond the time that women stopped taking the drug. The risks of stroke, deep-vein thrombosis, and cataracts - possible side-effects of tamoxifen treatment - were also similar to those reported previously.
"The BCPT should be viewed not only as the first study that demonstrated that breast cancer can be prevented, but also as a beginning from which a new paradigm for breast cancer prevention can evolve," said Bernard Fisher, M.D., first author of the initial and final reports, and principal investigator for the trial. "Cohorts of women at increased risk for breast cancer, who could derive a net benefit from receiving tamoxifen, have been clearly defined."
The BCPT was designed to see whether the drug tamoxifen could prevent breast cancer in women who were at an increased risk of developing the disease. Women in the study were randomly assigned to receive tamoxifen or a placebo, and neither participants nor their clinicians were aware of the treatment assignment, a process called double-blinding. Since 1998, BCPT participants have been followed by the NSABP, the Pittsburgh-based research network that conducted the trial with support from the National Cancer Institute (NCI), part of the National Institutes of Health.
When the initial results of the BCPT were first announced, scientists found a 49 percent reduction in invasive breast cancer (cancer that has spread and is growing into surrounding, healthy tissues) incidence among participants at increased risk for the disease who took tamoxifen (Nolvadex®, AstraZeneca Pharmaceuticals, Wilmington, Del.), a drug that had been used for over twenty years to treat breast cancer. The initial study results also showed a 45 percent reduction in non-invasive breast cancer incidence.
By 2005, after seven years of follow-up, investigators found that healthy women assigned to take tamoxifen developed 145 cases of invasive breast cancer compared to 250 cases in the women assigned to take placebo. This final analysis confirms that tamoxifen reduces the risk of invasive breast cancer in both pre- and post-menopausal women at increased risk for the disease. Additionally, risk of pulmonary embolism was 11 percent lower than initially reported and risk of endometrial cancer was about 29 percent higher, but neither of these differences was statistically significant.
"The NCI is very pleased with the ultimate results of the BCPT, in part because there is proof of a benefit from tamoxifen beyond the time a woman is taking the pills," said Leslie Ford, M.D., associate director for NCI's Division of Cancer Prevention and co-author of the study. "We hope that other breast cancer prevention clinical trials, such as STAR, the Study of Tamoxifen and Raloxifene, help us identify drugs that maximize the benefits and minimize the side effects for women interested in reducing their risk of developing breast cancer."
Launched in April 1992, the BCPT also looked at whether taking tamoxifen decreased the number of heart attacks and reduced the number of certain common types of bone fractures in these women. There was almost no difference in the number of heart attacks between the tamoxifen and placebo group, but women in the tamoxifen group had fewer bone fractures of the hip, wrist, and spine (80 cases in the tamoxifen group vs. 116 cases in the placebo group) as reported in 2005.
Only women at increased risk of developing breast cancer participated in the study. Because the risk of breast cancer increases with age, women 60 years of age and older qualified to participate based on age alone. At age 60, about 17 of every 1,000 women are expected to develop breast cancer within five years. Women between the ages of 35 and 59, who demonstrated an increased risk of breast cancer equivalent to or greater than that of an average 60-year-old woman, were also eligible.