Zoledronic acid is both safe and effective in preventing bone loss in postmenopausal women with breast cancer who are treated with aromatase inhibitors, according to data presented at the annual CTRC-AACR San Antonio Breast Cancer Symposium.

"Women who take aromatase inhibitors need some sort of bone protection, and this five-year data show that zoledronic acid is a viable option," said Dr. Adam Brufsky, associate professor of medicine, associate chief of haematolgy-oncology, and associate director for clinical investigation, University of Pittsburgh Cancer Institute.

Brufsky estimates that between 20,000 to 30,000 women a year will benefit from this therapy and that number is growing. Anastrozole, currently sold as Arimidex by AstraZeneca, is scheduled to go off patent within the next few years.

"Women who are on Medicare tend to go with tamoxifen because the cost of anastrozole puts them squarely in the donut hole of Medicare Part D, but once the cost barrier is removed there will likely be a mass switch to the aromatase inhibitor, which will necessitate the need for bone protection," said Brufsky.

Beyond the aging population, use of zoledronic acid could increase even further if the signs that it prevents breast cancer recurrence continue in larger studies.

Brufsky's study, Z-FAST (Zometa-Femara Adjuvant Synergy Trial), focused on 602 postmenopausal women with stage I to IIIa estrogen or progesterone receptor-positive breast cancer. The researchers randomized patients to immediate zoledronic acid or delayed zoledronic acid. The delayed group received it only if the T-score dropped below two or a clinical fracture occurred.

After five years, patients in the immediate treatment arm had a bone mineral density increase of 6.2 percent in their lumbar spine area, while those in the delayed arm had a decrease of 2.4 percent. In the hip area, the increase was 2.6 percent with immediate treatment compared with a 4.1 percent decrease with delayed treatment.

Fractures occurred in 10.7 percent of the patients treated immediately and 12.4 percent of the patients who received delayed treatment.

There were no serious renal events and no osteonecrosis of the jaw, which confirmed that the drug was safe and well tolerated.

Watch a press briefing by Prof Adam Brufsky on ecancertv here.