Osteoporosis Drug Found to Cut Breast Cancer Risk
A drug used to prevent osteoporosis in older women reduces the risk of breast cancer by as much as 70% without any serious side effects, researchers said Monday 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.
“This is a fantastic time for [breast] cancer prevention,” said Dr. Joseph Boyle of the European Institute for Oncology in Italy. “We are very clearly on the path to the future.”
“Coming on the heels of the recent tamoxifen study, this is very exciting news,” said Dr. Derek Raghavan of USC’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 quite different groups.
Tamoxifen was studied in women who are at higher than normal risk of developing breast cancer, and the study included women as young as 35. Raloxifene was studied in post-menopausal 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 has already scheduled a head-to-head trial of the two drugs that is expected to begin toward the end of the 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 of the disease. It is the second leading cause of cancer deaths in women after lung cancer, and the leading cause of death among women between 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% among women who were at high risk because of a family history of the disease.
That data was officially presented at the American Society for Clinical Oncology meeting.
Unfortunately, the drug also increased the risk of endometrial cancer and blood clots, which are normally rare. But experts noted that endometrial cancer has almost a 100% cure rate. The five-year survival rate for breast cancer ranges from 96.8% if the tumor is detected before it has spread to only 20.6% if it is not detected until it has spread to other parts of the body.
Because the mortality rate for breast cancer is so much higher than that for endometrial cancer, “the benefits [of tamoxifen] outweigh the risks relative to prevention, but women must be advised of the risks and benefits prior to making a decision,” Wolmark said.
Raloxifene is one of the first of the so-called designer estrogens, synthetic chemicals that researchers hope will have the benefits of estrogen without some of the risks.
The results with raloxifene, marketed as Evista by Eli Lilly & Co., came from a study designed to test its efficacy in reducing fractures caused by osteoporosis in older women. The study, led by Dr. Steven R. Cummings of UC San Francisco, studied 7,704 healthy women with low bone density and no family history of breast cancer.
Curiously, women with osteoporosis have only about one-third the normal risk of developing breast cancer, he noted. While this would put the study group at lower risk than the general population, the researchers believe the results of the study are valid because all the women in it had osteoporosis.
Two-thirds of the women in the study received raloxifene and the remainder got a placebo. Over a period of 29 months, there were 21 cases of breast cancer in the placebo group, compared to 11 cases in the treated group--which was twice as large. That translates to a 70% reduction in cases, somewhat larger than that observed with tamoxifen.
“That’s a very strong effect,” Cummings said.
There were only four cases of endometrial cancer in each group, he added, too small a number to determine if the drug might be exerting a protective effect there also. The risk for blood clots was the same in the two groups.
The researchers will continue the study for another four to five years to see how long the benefits persist, Cummings added.
Because the drug is already being marketed for use in preventing osteoporosis, physicians are free to prescribe it for any purpose they feel appropriate--including cancer prevention. But some experts, such as Dr. Michelle Curtis of the University of Texas’s Lyndon Johnson Hospital, warned against such use.
“This is exciting,” she said, “but all it really means is that we need to design trials looking specifically at breast cancer and raloxifene. We can’t extrapolate results from a study that wasn’t designed to look at that.”
Cummings countered that the results were so dramatic that they were extremely convincing, even if prevention of breast cancer was not the primary purpose of the study.
Curtis also urged that post-menopausal women who are already taking estrogen replacement therapy not abandon it in favor of raloxifene. Estrogen, she noted, has been found to provide a strong reduction in the risk of heart disease, while raloxifene has not. “And heart disease kills 10 times as many women as breast cancer,” she said.
* LIFE-SAVING TEST: A study says Prostate-Specific Antigen (PSA) test should cut such cancer deaths by 69%. B1
