Analyses at 62 months, or more than two years after treatment completion, confirm and extend the durable clinical and anticancer benefits of the bisphosphonate zoledronic acid that were reported at the 48-month follow-up in the Austrian Breast and Colorectal Cancer Study Group Trial 12 (ABCSG-12) trial.

In the ABCSG-12 trial, 1,803 premenopausal women with endocrine-responsive early breast cancer were randomized to goserelin (3.6 mg q28d) and tamoxifen (20 mg/d) or anastrozole (1 mg/d) ± zoledronic acid (4 mg q6mo) for 3 years.

The new results, released at the 33rd Annual San Antonio Breast Cancer Symposium. indicate that the benefits of combining zoledronic acid with adjuvant endocrine therapy in premenopausal women with hormone-responsive, early-stage breast cancer hold up long after therapy has been completed.

“Clinicians should consider combining zoledronic acid with adjuvant endocrine therapy in premenopaual women with early-stage, endocrine-responsive breast cancer,” principal investigator Michael Gnant, MD, professor of surgery at the Medical University of Vienna, advised.

Dr. Gnant reported that adding zoledronic acid (4 mg every 6 months) to endocrine therapy for three years produced durable disease-free survival (DFS) benefits in the anastrozole and tamoxifen groups and a strong trend towards improved overall survival at a median follow-up of more than two years after treatment completion, showing a carryover benefit.

He said that the anticancer effects of bisphophonates may modify the bone marrow microenvironment and thus contribute to the DFS survival results seen in and outside of bone.

At 62 months follow-up, the benefits of treatment with zoledronic acid inside and outside of bone included decreased bone metastases, decreased contralateral breast cancer, decreased locoregional and distant metastases, improved DFS, and a confirmed trend towards improved overall survival.

Zoledronic acid did not increase the occurrence of serious adverse events compared with endocrine therapy alone.

The European Society of Medical Oncology recently stated that zoledronic acid may be appropriate for preventing bone loss and reducing the risk of breast cancer recurrence in premenopausal women receiving endocrine therapy and in postmenopausal women receiving aromatase inhibitor therapy.

Endocrine-responsive disease accounts for 62% of breast cancer cases in premenopausal women, Dr. Gnant said.

Written by Jill Stein
Jill Stein is a Paris-based freelance medical writer.