The largest North American breast cancer prevention trial ever undertaken, the Study of Tamoxifen and Raloxifene (STAR), nears completion as the 18,000th woman joined the trial late last month. One thousand more women are needed to finish this important trial, which started in 1999 and is being carried out at more than 500 sites in the United States, Canada, and Puerto Rico. The 19,000th participant should be enrolled by July, five years after the study began.

STAR results could be ready as early as mid-2006, predict researchers from the National Surgical Adjuvant Breast and Bowel Project (NSABP), the network of investigators conducting the trial, and the National Cancer Institute (NCI), which is funding the study.

"Prompt completion of STAR will be a critical step in our ability to prevent breast cancer in women at increased risk of the disease," said Dr. Leslie Ford, associate director for clinical research in NCI's Division of Cancer Prevention, who oversees STAR.

The study is designed to determine whether raloxifene (Evista®), an osteoporosis prevention and treatment drug, is as effective as tamoxifen (Nolvadex®) in reducing breast cancer risk and if it has fewer side effects. It is the follow-up study to the landmark Breast Cancer Prevention Trial (BCPT), published in 1998, which led to tamoxifen being approved by the U.S. Food and Drug Administration for risk reduction in women at increased risk for developing breast cancer.

STAR includes postmenopausal women who are at increased risk for breast cancer due to a family history of breast cancer and a combination of personal medical factors. These factors are used to estimate a woman's individual risk for developing the disease in the next five years and in her lifetime.

Breast Cancer Risk of Women in the STAR Trial  Five-year Breast Cancer  Risk  % of Women in STAR Who  Fall into This Risk Category  1.7% - 1.9%  11.0  2.0%-2.9%  30.2  3.0%-4.9%  31.5  5.0% or greater  27.3  Age Range  % of Women in STAR in  This Age Range  35-49  9.2  50-59  49.7  60+  40.9

Originally, 22,000 postmenopausal women were sought for STAR. That number was based on volunteers having at least a 1.7 percent chance of developing invasive breast cancer within five years - about 17 women per 1,000. But STAR enrollees have about twice the minimum risk, or a 3.5 percent chance of developing cancer within that time period - 35 per 1,000 women - so the Data and Safety Monitoring Board (DSMB) overseeing the trial recommended a decreased study size. (See table).

"This greater risk means that fewer women are required to see prevention effects from the drugs," explained Dr. Norman Wolmark, chairman of the NSABP and of the Department of Human Oncology at Allegheny General Hospital in Pittsburgh, Pa. So, in October 2003, NCI and NSABP agreed with the DSMB recommendation that only 19,000 women would be recruited for STAR.

Women enrolled in STAR are randomly assigned to receive either 20 mg of tamoxifen or 60 mg of raloxifene daily. They also have regular follow-up examinations until the results of the trial are known.

The 18,000th participant, Maxine Watson of Mesquite, Tex., hopes that joining STAR through the Baylor-Sammons Cancer Center in Dallas will reduce her risk of developing breast cancer. "My sister is a breast cancer survivor, so my other sister and I decided to participate in STAR because we wanted to make a contribution to breast cancer research," said Ms. Watson. "Regardless if I am the first or the eighteen thousandth woman who joined, I feel it's a privilege and an honor to make a contribution to the STAR trial."

For more information about the study or to locate a STAR center in the United States and Puerto Rico, contact NCI's Cancer Information Service at 1-800-4-CANCER (1-800-422-6237). In Canada, contact the Canadian Cancer Society's Cancer Information Service at 1-888-939-3333.

Alternately, women can visit http://www.breastcancerprevention.com to calculate their breast cancer risk or find more information about STAR.