FRIDAY, June 3 (HealthDay News) -- Early stage breast cancer patients can see their chances of the cancer's return drop by 32 percent when the osteoporosis drug Zometa is added to regular hormone therapy for three years after surgery, Austrian researchers report.

Women undergoing hormone treatment for breast cancer are prone to develop osteoporosis, so they are usually given a bisphosphonate such as Zometa (zoledronic acid), to build bone strength. However, Zometa appears to have the additional benefit of reducing the risk of cancer recurrence, according to Dr. Otis Brawley, chief medical officer for the American Cancer Society.

"Aromatase inhibitors [like Arimidex] cause osteoporosis, and you must put a patient who is being put on an aromatase inhibitor on some type of osteoporosis preventive therapy," Brawley said. "This study says that putting a patient on Zometa may have even a bigger bang for the buck than the prevention of osteoporosis."

Although exactly how Zometa reduces the risk of recurrence isn't known, lead researcher Dr. Michael Gnant, a professor of surgery at the Medical University of Vienna, said he thinks "it prohibits dormant tumor cells in the bone marrow from 'waking up.'"

"Zometa actually hardens the bone and makes it more difficult for the cancer to actually implant," Brawley added.

The report was published in the June 4 online edition of The Lancet Oncology to coincide with the American Society of Clinical Oncology's annual meeting in Chicago, where the findings were to be presented Friday.

For the study, Gnant's team enrolled 1,803 premenopausal women with early-stage hormone-receptive breast cancer. The trial was funded by drug makers AstraZeneca and Novartis.

The women were randomly assigned to tamoxifen alone, tamoxifen plus Zometa, Arimidex (anastrozole) or Arimidex plus Zometa. Zometa infusions were given every six months during the three years of the trial.

The choice of hormone drugs is important, because while Arimidex is associated with a risk of developing osteoporosis, tamoxifen isn't. So women prescribed tamoxifen would not usually be given an osteoporosis drug, Brawley explained.

In 2009, after four years of follow-up, the researchers reported women receiving Zometa had a 36 percent reduction in the risk of a recurrence of breast cancer, compared with women not on the drug. There were also indications that Zometa extended overall survival, the researchers said.

The current report looks at more than five years of follow-up, which is more than two years after treatment with Zometa was stopped.

The researchers found that women receiving Zometa had substantially better disease-free survival (92 percent) than women receiving hormone therapy alone (88 percent). This is a 32 percent reduction in the risk of a recurrence of breast cancer among those who had received Zometa, they noted.

These results were seen among women taking either tamoxifen or Arimidex plus Zometa. However, overall survival was worse among women receiving Arimidex, they added.

The effect of Zometa was even more pronounced in women over 40, where the risk of the cancer's recurrence was cut by 42 percent.

In addition, Zometa was associated with a reduction in cancers developing in bone and other sites as well as breast cancer in the breast where cancer was found and in the unaffected breast, Gnant's group found.

The researchers added that Zometa was well-tolerated and side effects, which included joint pain, bone pain and fever, were relatively mild. There were also no cases of osteonecrosis of the jaw (death of bone in the jaw), which Zometa has been linked to when the drug is given for osteoporosis after major dental work, Brawley noted.

This study showed that "disease-free survival increased, it's not powered for overall survival," Brawley said. "There have been recent studies where disease-free survival was increased, but ultimately overall survival was not."

"This is something to consider," Brawley said. "I never change my practice based on one trial. But, I see very little harm in giving Zometa along with aromatase inhibitors. Many of the patients I take care of already get this anyway," he added.

In the United States, Zometa is sold to wholesalers for $844.10 per dose, according to Dana Kahn Cooper, a spokeswoman for AstraZeneca.

"As Zometa is a physician-administered drug by infusion, the cost to the consumer is generally their doctor visit co-pay, which varies based on insurance coverage," Cooper said. "Some patients have drug co-pay as well. We do not set retail prices. Price around the world varies by country."

More information

For more on breast cancer, visit the American Cancer Society.