San Antonio Breast Cancer Symposiumで発表された研究によれば、良く使用される骨粗鬆症治療薬が乳ガンのリスクを有意に減少させるという。|
New Weapon in Breast Cancer Battle? Experts Cautious
Studies Link Osteoporosis Treatment and Reduced Breast Cancer Risk, Experts Want More Info
By LEE FERRAN and KATE McCARTHY
Dec. 11, 2009
There might be link between a common osteoporosis treatment and a significantly reduced risk of breast cancer in women, according to two studies presented at the San Antonio Breast Cancer Symposium Thursday.
The first study from the Women's Health Initiative found that women who used bisphosphonates had 32 percent fewer cases of invasive breast cancer. The second, from a northern Israel study, found that women who used bisphosphonates for more than five years also had a 29 percent reduced risk of post-menopausal breast cancer.
Bisphophonates are drugs that can slow or stop the bone dissolving process that leads to osteoporosis. Popular examples of the medicines are drugs such as Fosamax, Boniva, Actonel and Reclast.
Dr. Richard Besser, ABC News' senior health and medical editor, said the lead researcher has a few theories about why the drugs could help reduce the risk.
"One is that these drugs could be toxic to the cancer cells themselves," Besser said on "Good Morning America."
"Another is that it could just interfere with the pathway by which women go on to develop breast cancer. But more work would need to be done in that area."
While experts are cautiously optimistic about the studies, several of them said that more information is necessary, and as of now, they would not suggest the use of bisphosphonates for women who do not have osteoporosis.
"These are very early studies showing a possible association, but without a good long-term follow-up," Dr. Sandhya Pruthi of the Mayo Clinic in Rochester, Minn., wrote in an e-mail. "However, bisphosphonates are drugs that also have side effects, so it is not something I would give to a patient who does not have osteopenia or osteoporosis to potentially prevent breast cancer at this time."
Besser agreed and advised women not to run out and buy osteoporosis treatments.
"These aren't ready for prime time," he said. "These studies were not done for this reason. So now they will do a big study and give half the women these drugs and another group of women not have these drugs and follow them over time to find out if it is truly protective."
But, Besser added, the findings hold hope.
"That's how some of the greatest discoveries come about, just by surprises like this," he said.
Bisphosphonates are "commonly used for the treatment of osteoporosis and for prevention and treatment of skeletal lesions due to malignancy," according to one of the studies' abstract descriptions.
Experts said they view the apparent breast cancer link as a favorable bonus to regular osteoporosis treatment.
"For women who need treatment for osteoporosis, these data suggest that there may be some secondary gain," Harold Burstein, breast oncologist at Dana-Farber Cancer Institute in Boston, said. "However, the data are not sufficient to suggest that bisphosphonate therapy would prevent breast cancer for ordinary women."
Data 'Should Justify' More Studies
Rather, one of the studies' greatest benefits could simply be increased interest in the positive effects of bisphosphonates, Burnstein said.
"The data should justify prospective studies to evaluate how important these interventions really are," Burnstein said.
The ABC News Medical Unit contributed to this report.
Bone Drugs Taken by Some Women May Lower Breast Cancer Risk, Studies Say
By RONI CARYN RABIN
Published: December 10, 2009
Drugs already taken by millions of healthy older women to prevent bone loss and broken hips may also protect them from breast cancer, according to two observational studies that found that women taking oral bisphosphonates developed about a third fewer breast cancers than other women.
The drugs are in the class of medications that includes the brand name drug Fosamax, now available generically as alendronate sodium.
The findings, presented Thursday at a scientific conference, are from a retrospective analysis of data from the Women’s Health Initiative, a federal study, and a separate Israeli observational study of several thousand postmenopausal women.
Neither study was a randomized clinical trial, and several top cancer doctors expressed skepticism about the findings, saying they prove only an association and may reflect the fact that women with bone problems who are most likely to take the medications have a lower breast cancer risk to begin with.
The research generated excitement at the conference, the annual San Antonio Breast Cancer Symposium, even before the official presentations on Thursday, because unlike other drugs that can be used prophylactically to prevent breast cancer, oral bisphosphonates are already widely used and do not cause hot flashes.
There was also a hint in the studies that the drugs might have a particular impact on curbing the kinds of tumors that are the most difficult to treat: those that are not fueled by estrogen.
“With tamoxifen and raloxifene, we have drugs that reduce estrogen receptor-positive tumors, but we’ve never had anything worth anything that prevented estrogen receptor-negative tumors,” said Dr. Gabriel N. Hortobagyi, who directs the breast cancer research program at the University of Texas M.D. Anderson Cancer Center.
But Dr. Hortobagyi said randomized controlled clinical trials were needed to prove the drugs have an effect, adding, “These are provocative data, but certainly not compelling, and not definitive.”
Other breast cancer experts agreed. “If in fact you have osteoporosis and you’re taking these drugs, it’s possible there is an added benefit,” said Dr. Eric P. Winer, a breast cancer specialist at the Dana-Farber Cancer Institute in Boston. “But at the moment, I don’t think these studies should be used as a reason to take a bisphosphonate to prevent breast cancer. As with all drugs, there are side effects and risks.”
About 10 million Americans have osteoporosis, many of them women. Last year more than 45 million prescriptions for oral bisphosphonates were filled in the United States, generating over $4.9 billion in sales, according to IMS Health, a health care information and consulting company. The drugs have been associated with a rare but very serious side effect: bone death, or osteonecrosis, of the jaw, in which part of the jawbone dies and becomes exposed.
The new research included an analysis of data from the Women’s Health Initiative, which included 151,592 postmenopausal women followed on average for 7.8 years, among them 2,216 who happened to be taking oral bisphosphonates at the beginning of the study.
There were 3.29 cancers per 1,000 women taking the drugs over the course of a year, compared with 4.38 cancers per 1,000 women not taking the drugs. After adjusting for different risk factors among those who were or were not taking the drugs, the analysis determined there were 32 percent fewer new breast cancers among users of oral bisphosphonates.
Dr. Rowan T. Chlebowski, the study’s author and a researcher at Harbor-U.C.L.A. Medical Center, said the drugs might have toxic effects on tumor cells or affect pathways that disrupt cell proliferation.
The second set of findings comes from a continuing population-based case-control study of 4,575 postmenopausal women in Israel that used interviews and pharmacy records to determine whether oral bisphosphonates were used before a cancer diagnosis. It found that women who used the drugs for over a year had a 29 percent relative reduction in risk for breast cancer, and that tumors that developed among users were more likely to be estrogen receptor-positive.
“We’re reporting an association,” said the study author, Dr. Gad Rennert of the Technion-Israel Institute of Technology. “If the story is right and true ― and I’ll repeat this 100 times, because in science you never know, I think it is but I can’t guarantee it ― it’s quite meaningful.”
Dr. Rennert said the research was bolstered by a study published in The New England Journal of Medicine this year that reported that premenopausal breast cancer patients who had infusions of a bone-loss drug called zoledronic acid were a third less likely to have a recurrence and metastases than women who did not get it. Users of the drug were also less likely to develop a new cancer in the opposite breast.
Bisphosphonates are already widely used in the management of breast cancer patients to counter bone loss associated with hormonal therapy and to decrease pain and bone complications in advanced cancer. Recent reports have suggested that the drugs’ effects on bone appear to inhibit the spread of cancer to the bone and improve survival.
But experts warn there is ample reason for caution in interpreting the new studies. Older women who take oral bisphosphonates generally do so because they have low bone mineral density. But women with that condition may be at lower risk for developing breast cancer in the first place; their bone problems are believed to stem from lower estrogen levels, and breast cancer risk increases with higher lifelong exposure to estrogen.
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