A drug currently used to treat and prevent osteoporosis may be the newest drug in the fight against breast cancer.
The initial results of a study comparing the drugs tamoxifen, a drug commonly taken to prevent breast cancer, and raloxifene, a drug used to treat and prevent osteoporosis, has shown that both cut in half a woman's risk of developing breast cancer after menopause. However, while many worry about tamoxifen's serious side effects, such as uterine cancer and blood clots, raloxifene, sold under the name Evista, seems to be a safer choice.
The study, sponsored by NCI, included almost 20,000 postmenopausal women at an average age of 58 who were considered at high risk for breast cancer. Half of the women took tamoxifen, the other half raloxifene, each once daily. After five years, only about 165 women from each group developed invasive breast cancer, half the number expected if the women did not take either drug.
There are several factors that contribute to one's risk of developing breast cancer, including increasing age, family history of the disease, having no children, previous breast biopsies and having one's first period at an early age. It is estimated that about 9 million postmenopausal women are at high risk for developing breast cancer, and about four percent of these women will develop breast cancer within five years.
However, many women are hesitant to take tamoxifen because it has been shown to increase a woman's risk of developing uterine cancer and life-threatening blood clots. In fact, 87 women in this study who were taking tamoxifen developed a serious blood clot and 36 developed uterine cancer.
The numbers were more positive for raloxifene.
Among the women who took raloxifene only 65 developed blood clots—29 percent fewer than those taking tamoxifen. Additionally, only 23 women taking raloxifene developed uterine cancer—36 percent fewer than the tamoxifen group. The most common side effects of raloxifene reported by the women were hot flashes and leg cramps. Although few, women in both groups had an equal number of strokes and heart attacks.
"Although no drugs are without side effects, tamoxifen and raloxifene are vital options for women who are at increased risk of breast cancer and want to take action," said Dr. Leslie Ford, associate director for clinical research at the NCI's Division of Cancer Prevention. "For many women, raloxifene's benefits will outweigh its risks in a way that tamoxifen's benefits do not."
One drawback to raloxifene is that it does not seem to decrease the risk of two types of early-stage breast cancer. While both of these cancers can usually be cured, tamoxifen did decrease the risk of developing them in the first place by half.