Zoledronic acid reduces recurrence in women with early-stage breast cancer undergoing hormone therapy

Researchers report at ASCO 2008 that zoledronic acid (Zometa), a drug used to treat bone metastases and recently approved to treat osteoporosis, also lowers the risk of breast cancer recurrence in premenopausal patients with early-stage disease who have undergone surgery and are receiving ovarian suppression and hormone therapy. All women in this multicentre phase III trial had cancer that was oestrogen-receptor-positive or progesterone-receptor-positive.

Recent studies have shown that zoledronic acid, a bisphosphonate drug, can reduce bone loss caused by cancer treatments. Preclinical research suggested the drug might also have an anticancer effect.

"It's very exciting to find that in addition to preventing bone loss in women undergoing adjuvant endocrine therapy for breast cancer, zoledronic acid can also reduce the likelihood that breast cancer will return in some women," said Michael Gnant, MD, a professor of surgery at the Medical University of Vienna, the president of the Austrian Breast and Colorectal Cancer study group, and the study's lead author. "Future research will focus on optimizing the administration schedule and the dose, and determining which patients will benefit the most from treatment with zoledronic acid."

The study enrolled 1,803 patients who were undergoing drug-induced ovarian  suppression (using goserelin), who previously had surgery to remove the primary tumour and whose cancer had spread to ten or fewer lymph nodes. The study had four arms: treatment with the hormone therapies tamoxifen or anastrozole, with or without zoledronic acid. Tamoxifen is given as a standard adjuvant treatment after surgery in both pre- and post-menopausal women who have hormone-responsive tumours. Anastrozole also is approved for hormone-responsive tumours, but only in post-menopausal women, a condition that ovarian suppression with goserelin simulates.
The study's primary endpoint was disease-free survival - the length of time after treatment in which no disease is found. After a median follow-up of 60 months, the researchers found that hormone therapy plus zoledronic acid reduced the risk of relapse by 35 percent compared with hormone therapy alone. They did not find a significant difference between the two hormone therapies. The treatment was well tolerated in all four groups and there were no unexpected side effects.