SAN ANTONIO – Adding zoledronic acid to adjuvant endocrine therapy significantly improves disease-free and overall survival in premenopausal women with endocrine-receptor–positive early breast cancer at 7 years’ follow-up, Dr. Michael Gnant reported today at the San Antonio Breast Cancer Symposium.
Women in the ABCSG (Austrian Breast and Colorectal Cancer Study Group)-12 trial randomized to receive zoledronic acid in addition to ovarian function suppression and endocrine therapy had a 28% reduction in risk of recurrence and 37% reduction in mortality risk at 84 months, compared with women randomized to adjuvant endocrine therapy alone, according to Dr. Gnant, professor of surgery at the Medical University of Vienna.
The findings confirm data previously reported by the ABCSG-12 investigators demonstrating disease-free and overall survival benefits associated with the treatment regimen at 48 and 62 months of follow up (Lancet Oncol. 2011;12:631-41). "The continued success of this treatment means we can intervene early and still observe persistence of the benefit of treatment," said Dr. Gnant, president of the ABSCG.
The four-arm open-label trial randomly assigned 1,803 women to ovarian suppression and endocrine therapy plus or minus zoledronic acid for 3 years. Investigators used log-rank tests and Cox models to evaluate disease-free survival and overall survival, Dr. Gnant explained.
All of the patients, mean age 44.5 years, were premenopausal and had undergone surgery for stage I or II hormone receptor–positive breast cancer. They were treated for 3 years with 3.6 mg subcutaneous goserelin every 28 days, and randomized to 20 mg of oral tamoxifen daily plus placebo, 1 mg of oral anastrozole daily plus placebo, or either of the latter with 4 mg intravenous zoledronic acid every 6 months.
Dr. Michael Gnant_
At a median 84 months’ follow-up, the hazard ratios for breast cancer recurrence and death, respectively, for women receiving adjuvant zoledronic acid were .72 and .63, Dr. Gnant reported, noting that the reductions remained significant in univariate and multivariate analyses. Further, in multivariate analysis, "there was no interaction between zoledronic acid and tumor parameters or endocrine therapy," he said. "The hazard ratios were identical for small and large tumors, node-positive and node-negative tumors, and for patients receiving anastrozole and tamoxifen."
There was a strong interaction between zoledronic acid and age in terms of survival benefit, however, with patients older than 40 years experiencing a 34% reduction in recurrence risk and a 44% reduction in mortality, according to Dr. Gnant. No similarly significant survival benefits were observed among patients younger than 40 years, he said.
As expected, patients receiving zoledronic acid experienced more arthralgia, Dr. Gnant stated, "but, importantly, there were no cases of osteonecrosis of the jaw and no renal failure in the treatment population."
The findings, which are consistent with those seen in the postmenopausal cohort of the AZURE trial, "suggest that estrogen deprivation and reduction of bone turnover-derived growth factors in the bone marrow microenvironment are needed to sufficiently suppress dormant micrometastases," Dr. Gnant explained. Together with the known bone-protective benefits of zoledronic acid, the new data provide sufficient support for adding the bisphosphonate to adjuvant endocrine therapy in premenopausal women with early endocrine-receptor–positive breast cancer, he said.
Dr. James N. Ingle of the Mayo Clinic in Rochester, Minn., the discussant for the session, concluded that the ABCSG-12 findings provide level-one evidence for the value of adding zoledronic acid to goserelin and tamoxifen or anastrozole in this patient population. "Zoledronic acid as standard of care [in these patients] will be more widely accepted when the results of the ongoing SOFT [Suppression of Ovarian Function trial] are reported," which will clarify the value of tamoxifen vs. exemestane (Aromasin) in conjunction with ovarian suppression, he said.
Dr. Gnant and Dr. Ingle reported having no relevant financial disclosures.