A class of drugs that has been increasingly used to treat breast cancer in recent years may not improve survival rates in younger women with the disease, researchers reported Thursday.
The medications — bone-building drugs called bisphosphonates — have generated enthusiasm among cancer researchers because of their potential to slow the growth of cancer cells in bone and improve bone strength. But a large study on a potent bisphosphonate called zoledronic acid, or Zometa, found that the drug did not improve survival for patients with early stage breast cancer except among a subset of women who were five or more years past menopause.
Although more research is needed, the study, presented at the annual meeting of the San Antonio Breast Cancer Symposium, supports the drug's potential merits for older, postmenopausal women but raises questions about whether premenopausal or early menopausal women will benefit.
Several other studies on bisphosphonates and breast cancer are ongoing, and their results will be needed to resolve the question, said Dr. Sharon Giordano, an associate professor of medical oncology at the University of Texas MD Anderson Cancer Center who was not involved in the study.
"The difference in outcome by menopausal status is very intriguing but not definitive," she said. "This won't be the final word."
Bisphosphonates are used to treat osteoporosis. In addition, however, they have been used to treat bone disorders that arise in people with metastatic breast cancer — cancer that has spread elsewhere in the body — because breast cancer cells often migrate to bone. Once inside the bone tissue, the drugs are thought to interfere with the tendency of cancer cells to affix to the bone, thus slowing progression of the disease.
Last year, a study suggested that the medications may also benefit women with earlier-stage breast cancer. The Austrian Breast and Colorectal Cancer Study, reported in the New England Journal of Medicine, found that adding zoledronic acid to standard breast cancer therapy reduced recurrences by 36% in premenopausal women with breast cancer. Since then, bisphosphonate treatment has become much more common in the care of women with breast cancer.
The new study, nicknamed the AZURE trial, included 3,360 patients from 174 medical centers. All patients had stage II or stage III breast cancer, which means the cancer may be in lymph nodes but not in other organs. The participants ranged in age and menopausal status. They were assigned standard treatment for breast cancer or the standard treatment plus zoledronic acid for five years.
Women treated with zoledronic acid did not have increased survival rates overall except for the 1,101 women five or more years past menopause. This group had a 29% reduced risk of dying of the disease compared withsimilar women who did not take zoledronic acid.
Experts disagree on why the new results differ from those of the 2009 study.
Some scientists suspect it's because the patient groups and treatments were slightly different. Women in the Austrian trial had an earlier-stage disease than those in the AZURE trial, and most did not undergo chemotherapy, unlike the patients in the AZURE study.
In addition, the women in the Austrian study received drugs to stop estrogen production and put them into menopause. The level of estrogen in bones could affect how well bisphosphonates work to prevent cancer recurrence, said the lead author of the AZURE study, Dr. Robert Coleman, professor of medical oncology at the University of Sheffield in England.
"We need to understand why" the two studies differed, Coleman said. "I don't believe one is right and one is wrong."