Prevention of anastrozole induced bone loss with monthly oral ibandronate: Final 5 year results from the ARIBON trial

Purpose: The ARIBON trial is a double blind, randomised, placebo controlled study designed to evaluate the impact of ibandronate on bone mineral density (BMD) in women taking anastrozole for adjuvant treatment of breast cancer.

Methods: 131 postmenopausal women with early breast cancer were recruited to the study. Of these, 13 had osteoporosis, 50 osteopenia and 68 normal BMD. Patients with osteoporosis at baseline were treated with monthly oral ibandronate 150 mg for 5 years; osteopenic patients were randomised to receive either ibandronate or placebo for two years and offered open label ibandronate depending upon the results of their 2-year BMD result.

Results: Of the 20 patients with osteopenia who were randomised to ibandronate and evaluable at the 2 year visit, 17/20 were not offered a bisphosphonate and the improvements in BMD accrued during the first 2 years were lost both at the LS (-3.21%) and TH (-5.0%). Of the 16 patients randomised to placebo 8/16 with high rates of bone loss during years 0-2 received ibandronate over the next 3 years with improvements in BMD of +5.01 and +1.19 at the LS and TH respectively. The 8 patients who were not offered a bisphosphonate experienced relatively little change in BMD throughout the 5 years of the study (LS +0.15%, TH -2.72%). BMD increased steadily in the 9/13 patients initially identified as having osteoporosis (LS +9.65%, TH +2.72%).

Conclusions: Monthly oral ibandronate provides an option to clinicians considering use of a bispho-sphonate to prevent bone loss during aromatase inhibitor therapy.