A Boost For Breast Cancer Prevention
Tuesday, April 18, 2006
A drug used to prevent bones from thinning also offers millions of older women a powerful way to protect themselves against breast cancer, a large government-sponsored study has found.
The study of nearly 20,000 postmenopausal women found that raloxifene reduces their chance of developing breast cancer as effectively as tamoxifen, the only drug previously shown to reduce the risk, but is less likely to cause serious side effects such as uterine cancer and blood clots.
The findings indicate that raloxifene, sold under the brand name Evista, is a safer alternative for the estimated 9 million postmenopausal U.S. women at increased risk for breast cancer, experts said.
"This is good news for women," said Leslie Ford of the National Cancer Institute, which sponsored the $88 million study and released the preliminary findings early because of their public health implications. "Women now have a new option."
Because an estimated 500,000 women use raloxifene to reduce the risk of osteoporosis, many will be more comfortable using it for breast cancer protection, several experts predicted.
"It's terrific," said Susan Love, a breast cancer expert at the University of California at Los Angeles. "This gives us another drug that we can use to prevent breast cancer that is less risky than the only other drug we had."
Several experts, however, urged caution, saying that the advantage of raloxifene remains unclear and that more research is needed to prove the drug reduced the overall risk over longer periods.
"We need to understand who would be most likely to benefit. All drugs have side effects. We want to avoid exposing women to powerful drugs unnecessarily," said Carolina Hinestrosa of the National Breast Cancer Coalition, an advocacy group.
Eli Lilly and Co. said it would ask the Food and Drug Administration to approve Evista for breast cancer prevention in postmenopausal women, but doctors are free to prescribe it for that purpose immediately because the drug is already marketed for osteoporosis.
"I suspect a lot more women will be willing to take this drug," said Patrick Borgen of Memorial Sloan-Kettering Cancer Center in New York. "People see tamoxifen as a cancer treatment drug. When it comes to prevention, people don't want to be thought of as patients. This may be seen much more as a prevention drug."
Breast cancer strikes more than 211,000 U.S. women each year and kills more than 40,000, making it the leading cause of cancer and second-leading cancer killer among women.
Tamoxifen and a new class of drugs known as aromatase inhibitors can reduce the risk of breast cancer's recurrence, but tamoxifen is the only drug that had been shown to prevent tumors in the first place, cutting the chances by about half. It is not widely used for preventing primary tumors, though, mainly because it carries an increased risk of uterine cancer and blood clots.
Raloxifene works similarly to tamoxifen by blocking the effects of the hormone estrogen on breast tissue. To see whether it might be as effective as tamoxifen at reducing the risk of primary breast cancer, researchers gave 19,747 postmenopausal women either 60 milligrams of raloxifene or 20 milligrams of tamoxifen every day for five years. All were at increased risk of breast cancer because of their age, family history or other reasons. The study is the largest to test any drug for breast cancer prevention.
A preliminary analysis of the data found no difference in the number of invasive breast cancers in the two groups, indicating that raloxifene also cuts the risk by 50 percent. There were 167 invasive cancers in the raloxifene group and 163 in the tamoxifen group. About 320 women in each group would have been expected to develop breast cancer.
But the women taking raloxifene experienced 36 percent fewer uterine cancers (23 vs. 36) and 29 percent fewer blood clots (100 vs. 141). They were also less likely to develop cataracts.
"Raloxifene clearly has less toxicity and fewer side effects," said D. Lawrence Wickerham of the National Surgical Adjuvant Breast and Bowel Project in Pittsburgh, which led the study. "It's very exciting."
The findings, which do not necessarily apply to premenopausal women, will be published in a peer-reviewed journal and presented at a meeting of the American Society of Clinical Oncology. They were released early to give the participants a chance to switch drugs and to alert the public about the findings, officials said.
Although other researchers agreed the findings are promising, some were more cautious. Several noted, for example, that the study found that women taking raloxifene had no decrease in risk for very early forms of breast cancer known as ductal carcinoma in situ and lobular carcinoma in situ.
"If you want to show a long-term reduction in invasive cancer, you need to show a decrease in pre-invasive cancer," said Paul Goss of Harvard Medical School.
Others noted that it remains unclear whether the overall net benefit of the drug outweighs the net risks.
"I would call this a modest advance," said Carol Fabian of the University of Kansas.
But the researchers who conducted the study estimated that if every eligible woman used the drug, it would protect more than 2 million from developing life-threatening health problems.
"This gives women a real choice for reducing their risk for two of the major causes of morbidity and mortality as they age -- osteoporosis and breast cancer," Ford said.
Raloxifene costs about $75 for a one-month supply; tamoxifen costs about $100 for the same amount, officials said.