Researchers have proven the continuing effectiveness of treating patients with estrogen receptor-positive premenopausal breast cancer with adjuvant zoledronic acid in addition to adjuvant endocrine treatment including ovarian function suppression.

Data from the Austrian Breast & Colorectal Cancer Study Group (ABCSG-12), reported at the 2011 CTRC-AACR San Antonio Breast Cancer Symposium, held Dec. 6-10, 2011, confirmed and extended data reported at 48 months and 62 months of follow-up. Now at 84 months of follow-up, patients are experiencing drastically fewer recurrences of breast cancer and improved rates of survivorship without toxic side effects.

"We have confirmed what this trial showed initially, which was both exciting and surprising," said Michael Gnant, M.D., professor of surgery and president of the ABCSG at the Medical University of Vienna. "The continued success of this treatment means we can intervene early and still observe persistence of the benefit of treatment."

In the four-arm trial, researchers randomly assigned 1,803 premenopausal patients with early-stage, estrogen receptor (ER)-positive breast cancer to receive tamoxifen or anastrazole or each of these two treatments with zoledronic acid for three years. In the initial report, presented in 2008, Gnant and his colleagues reported significantly improved disease-free survival.

The most recent long-term data, at 84 months after treatment, revealed a 28 percent reduced risk for recurrence and a 36 percent reduction in risk for death among patients treated with zoledronic acid. Also, no patients experienced osteonecrosis of the jaw or renal failure ― thus, Gnant said, proving the safety of the treatment seven years later.

Researchers also found that patients aged older than 40 years with presumed complete ovarian blockade had a 34 percent reduced risk for recurrence and a 44 percent reduced risk for death. They found no significant survival benefits among patients aged younger than 40 years.

Gnant and his team said these data, considered with previously demonstrated bone-protective effects of zoledronic acid, suggest that adding zoledronic acid to adjuvant endocrine therapy including ovarian function suppression should be considered for premenopausal women with ER-positive early breast cancer.