The osteoporosis drug lasofoxifene statistically reduced the overall risk of breast cancer, as well as estrogen receptor positive invasive breast cancer in postmenopausal women with low bone density, according to a study published online Nov. 4 in The Journal of the National Cancer Institute.
The study, led by Dr. Andrea LaCroix of the Public Health Sciences Division, followed 8,556 postmenopausal women with low bone density and normal mammograms in a double-blind trial. The participants were randomly assigned to varying doses of lasofoxifene or placebo.
Like tamoxifen, lasofoxifene is a selective estrogen receptor modulator that blocks the effects of estrogen in breast tissue. Another SERM, raloxifene, has also been shown to reduce breast cancer risk.
The researchers found that the women taking 0.5 milligrams of lasofoxifene, compared to the placebo, had a statistically significant reduced risk of total breast cancer by 79 percent; the risk of estrogen receptor positive breast cancer was also reduced by 83 percent. Furthermore, there was a 32 percent reduction in coronary events, and a 36 percent reduction in strokes. Vertebral fractures also decreased by 42 percent, and nonvertebral fractures by 24 percent. The drug was previously shown to reduce the risk of estrogen receptor positive breast cancer.
Women with higher baseline estradiol levels were statistically significantly more likely to benefit from lasofoxifene compared to those with lower levels, although both groups had lower incidence of total breast cancer when treated with the drug.
'An attractive option'
The authors said the risk reduction for breast cancer with lasofoxifene was similar to that reported for tamoxifen and raloxifene. However, lasofoxifene posed fewer safety concerns than tamoxifen and provided more benefits than raloxifene.
Lasofoxifene may therefore have more potential benefits than the other SERMS. “The spectrum of activity for lasofoxifene, including the clinically and statistically significant reductions of nonvertebral fractures, stroke and serious heart events, makes it an attractive option, particularly for use in postmenopausal women with osteoporosis or higher estradiol levels,” the authors wrote.
They also point out some limitations of the study: the small number of incident breast cancer cases; the lack of follow-up data after five years; and the lack of comparative data on the efficacy of lasofoxifene to reduce stroke and other coronary events and fractures compared to other SERMS.
In an accompanying editorial, Dr. Victor Vogel of the Geisinger Medical Center called the reductions in breast cancer incidence and the stroke event rate particularly “dramatic.” He added that lasofoxifene might represent the long-awaited “tipping point” in breast cancer chemoprevention.
“We need more complete information about the long-term effects of lasofoxifene on both beneficial and unfavorable outcomes, but the early data regarding its risks and benefits are encouraging,” Vogel wrote.
Pfizer, Inc funded the study.
[Adapted from a JNCI news release]