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Adapted from the NCI Cancer Bulletin, vol. 5/no. 12, June 10, 2008 (see the current issue).

The addition of zoledronic acid (Zometa®) to adjuvant endocrine therapy in premenopausal women with early stage breast cancer significantly improves clinical outcomes beyond those achieved with endocrine therapy alone, researchers reported at the 2008 annual meeting of the American Society of Clinical Oncology. The results are from a phase III randomized trial of 1,800 women conducted by the Austrian Breast and Colorectal Cancer Study Group.

Zoledronic acid, part of a class of drugs known as bisphosphonates, is already used to treat bone metastases, and this trial was conducted based on data from preclinical and early phase trials indicating that the drug can also shrink tumors and block metastatic activity. The results bear this out, said principal investigator Dr. Michael Gnant from the Medical University of Vienna.

Overall, the trial showed no difference in disease-free survival between women treated with tamoxifen or anastrozole. But the addition of zoledronic acid to either therapy decreased the risk of a disease-free survival event by 36 percent compared with hormone therapy alone, Dr. Gnant said. At a median follow-up of 60 months, overall disease-free survival was 92.4 percent and overall survival was 97.7 percent.

Women in the trial - all of whom were premenopausal with stage I or II breast cancer that was responsive to endocrine therapy - were treated with surgery and, if needed, radiation therapy. They also received the drug goserelin to temporarily suppress the function of the ovaries. Each was randomly assigned to one of four adjuvant therapy arms: tamoxifen alone, the aromatase inhibitor anastrozole alone, or either drug plus zoledronic acid. Treatment lasted three years.

The drug was also well tolerated, with no indication of increased risk of liver problems or damage to the jaw bone - two side effects which have been associated with higher doses of bisphosphonate drugs.

[Note: Results from a smaller bone-density substudy of this trial were published in 2007.]

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