Long-term follow-up data from the Austrian Breast & Colorectal Cancer Study Group (ABCSG-12) suggest that anticancer benefits of adjuvant zoledronic acid result in highly significant disease-free and overall survival mainly in patients with low levels of estrogen, including women with ovarian suppression and who are older than 40 years.

Presented at the CTRC-AACR San Antonio Breast Cancer Symposium, held December 6-10, 2011, in San Antonio, Texas, the ABCSG-12 data confirmed and extended findings reported at 48 months and 62 months of follow-up. Now at the 84-month mark, women receiving adjuvant zoledronic acid in addition to adjuvant endocrine treatment, including ovarian function suppression, are experiencing drastically fewer recurrences of estrogen receptor (ER)–positive premenopausal breast cancer.

“We have confirmed what the trial showed initially, which was both exciting and surprising,” commented Michael Gnant, MD, professor of surgery and president of the ABCSG at the Medical University of Vienna (Austria), in a statement detailing his group’s latest results.

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Gnant and colleagues randomized 1,803 premenopausal women with early-stage, ER-positive breast cancer to receive either tamoxifen or anastrazole, either with or without zoledronic acid, for 3 years. In 2008, the investigators reported significantly improved disease-free survival; the current results show a 28% reduced risk for recurrence and reduced mortality of 36% among the users of zoledronic acid, a bisphosphonate. No patients experienced jaw osteonecrosis or renal failure, indicating that the treatment is safe 7 years later.

Survival benefits were not significant for women younger than 40 years. However, those older than 40 years with presumed complete ovarian blockade had a 34% reduced risk for recurrence and a 44% reduced risk for death.