WASHINGTON — Cancer researchers Tuesday announced the start of a large-scale breast cancer prevention study pitting tamoxifen--approved last fall to reduce the risk of the disease--against a newer drug, raloxifene, which is used to prevent osteoporosis.
Scientists hope that raloxifene will prove more effective with fewer serious side effects than tamoxifen, which is known to raise the risk of endometrial cancer.
The nationwide trials, which could take up to 10 years, ultimately could provide high-risk women with a choice of medications to stave off the onset of the most commonly occurring--and probably the most feared--cancer in women.
About 180,000 new cases of breast cancer are diagnosed annually, with about 44,000 deaths. The leading cause of death among women is heart disease, and lung cancer is the leading cause of death from cancer for women.
A little more than a year ago, the first prevention study--which compared taking tamoxifen with taking nothing--showed that the drug reduced the risk of developing breast cancer by nearly half. Since then, findings from osteoporosis studies have suggested that raloxifene might have the same effect in preventing breast cancer--and possibly may be safer.
The question researchers--and women--will be asking now: Which one is better?
"Our hope is that raloxifene will prove to be more effective with fewer side effects," said Dr. Lawrence Wickerham, director of the National Surgical Adjuvent Breast and Bowel Project, a network of researchers supported by the federal government's National Cancer Institute.
"This will be the first fair head-to-head comparison," said Dr. Patricia Ganz of UCLA's Jonsson Comprehensive Cancer Center, one of five Los Angeles area health centers participating in the trial. "Until you actually test it in a population at high risk for breast cancer, we won't know."
But some groups have criticized such prevention studies because they involve giving otherwise healthy women drugs that carry potential dangers.
"Tamoxifen has not been shown to save lives of healthy women, nor has it been shown to prevent breast cancer indefinitely," the National Women's Health Network said in a statement.
Instead, taking these drugs may be "substituting one disease for another," the group said.
Raloxifene, sold under the brand name Evista, is made by Eli Lilly and Co. of Indianapolis. Tamoxifen, marketed as Nolvadex, is made by Zeneca Pharmaceuticals of Wilmington, Del.
The two drugs act similarly by interfering with the activity of the female hormone estrogen, which promotes the growth of breast cancer cells.
Both drugs share the risk of some side effects, the most serious being blood clots in veins and lungs. But tamoxifen also can contribute to the development of endometrial cancer, whereas raloxifene does not appear to have that effect.
Researchers cautioned, however, that raloxifene has been studied for only a short time. Tamoxifen has been in use for more than 20 years to treat breast cancer--long before it was approved for prevention.
The trial, one of the largest ever, will cost up to $100 million and involve about 22,000 high risk women in sites nationwide and in Canada and Puerto Rico. There are 20 sites in California. The other Los Angeles area centers include City of Hope Cancer Center, Cedars-Sinai Medical Center, St. Vincent's L.A. Oncologic Institute and USC/Norris Cancer Center.
Only postmenopausal women with multiple risk factors will be allowed to participate. These factors include age; number of first-degree relatives (mother, sister, daughter) with breast cancer; never having had children, or first delivery at a later age; early onset of menstrual periods; late menopause; and how many breast biopsies a woman has had.