Final Results from the NSABP Breast Cancer Prevention Trial Reported
Researchers 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 physicians 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, researchers 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.
###
For information on the National Surgical Adjuvant Breast and Bowel Project
clinical trials, go to
http://www.nsabp.pitt.edu. For women interested in
learning about future breast cancer prevention trials, go to
http://www.breastcancerprevention.com.
For more information about cancer, visit the NCI Web site at
http://www.cancer.gov or call NCI's Cancer Information Service at 1-800-4
CANCER (1-800-422-6237).
*B. Fisher, J.P. Costantino, D.L. Wickerham, R.S. Cecchini, W.M. Cronin, A.
Robidoux, T.B. Bevers, M.T. Kavanah, J. Atkins, R.G. Margolese, C.D. Runowicz,
J.M. James, L. G. Ford, N. Wolmark. Tamoxifen for Prevention of Breast Cancer:
Current Status of the National Surgical Adjuvant Breast and Bowel Project P-1
Study. Journal of the National Cancer Institute, Vol. 97, No. 22, November 16,
2005.
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