LOS ANGELES -- A drug used to prevent osteoporosis in older women reduces the risk of breast cancer by as much as 70 percent without any serious side effects, researchers said yesterday at a meeting of the American Society for Clinical Oncology in Los Angeles.
The risk reduction produced by the drug, called raloxifene, is about the same as that reported earlier this year for tamoxifen, but the latter drug can increase the risk of endometrial cancer and blood clots.
"Coming on the heels of the recent tamoxifen study, this is very exciting news," said Dr. Derek Raghavan of the University of Southern California's Norris Comprehensive Cancer Center. "However, these drugs are not for every woman. Before advocating their widespread use, further trials must be conducted to determine if these drugs actually prevent breast cancer, or merely delay it."
Physicians also cautioned that women who are already taking tamoxifen should not rush to switch to raloxifene, because the two drugs were tested in different groups.
Tamoxifen was studied in women who were at higher-than-normal risk of developing breast cancer, and the study included women as young as 35. Raloxifene, in contrast, was studied in postmenopausal women who had a lower-than-normal risk.
"We just don't know what the rate of risk reduction [with raloxifene] is going to be in the high-risk group," said Dr. Norman Wolmark, chairman of the National Surgical Adjuvant Breast and Bowel Project.
To find that out, the National Cancer Institute already has scheduled a head-to-head trial of the two drugs that is expected to begin toward the end of this year. "We certainly hope that raloxifene will live up to the promising preliminary data," Wolmark said.
In 1998, 215,700 new cases of breast cancer will be diagnosed and 43,500 women will die from the disease. It is the second leading cause of cancer death in women, after lung cancer, and the leading cause of death among women between the ages of 40 and 55.
The current round of excitement was triggered April 6 when the National Cancer Institute reported that tamoxifen, a drug used for 25 years to treat breast cancer, was the first agent found to prevent the disease. Marketed by Zeneca Pharmaceuticals as Nolvadex, the drug was shown to reduce the risk of breast cancer by 45 percent among women who were at high risk because of a family history of the disease.
Pub Date: 5/19/98