Effect of monthly oral ibandronate on anastrozole-induced bone loss during adjuvant treatment for breast cancer: One-year results from the ARIBON study

Abstract

553 Background: The aromatase inhibitor anastrozole is a highly effective treatment for breast cancer with superior efficacy and tolerability advantages over tamoxifen. However its use is associated with significant declines in bone mineral density (BMD) with an increase in fracture risk. The ARIBON trial is a double blind, randomised, placebo-controlled study designed to evaluate the impact of bisphosphonate treatment on BMD in women taking anastrozole. The study also aims to explore the relationship between levels of biochemical markers of bone metabolism with longer term changes in BMD as measured by Dual energy Xray Absorptiometry (DXA). Methods: 131 postmenopausal, surgically treated breast cancer patients were recruited from oncology clinics in Leeds and Sheffield, UK. Following consent, baseline bone densitometry showed that 68, 50 and 13 patients were found to be normal (T >-1.0), osteopenic (T -1.0 to -2.5) and osteoporotic (T < -2.5) respectively. All patients were treated with anastrozole 1mg once a day and offered calcium and vitamin D supplementation. In addition, osteopenic patients were randomised on a 1:1 basis to receive either treatment with ibandronate 150 mg orally every month or placebo. Osteoporotic patients were treated with open label ibandronate orally 150mg every month. Results: After I year, osteopenic patients treated with ibandronate gained +2.78% (range -3.8, +15.1) and +1.35% (range -4.1, +5.6) at the lumbar spine and hip respectively. Patients treated with placebo however lost -2.61% (range -11.0, +2.2) at the lumbar spine and -2.34% (range -10.4, +5.2) at the hip. The differences between the two treatment arms were statistically significant at both sites (p<0.001, independent samples t-test). Patients with osteoporosis gained +5.05% (range -8.7, +15.2) at the lumbar spine and +2.62% (range -1.0, +8.6) at the hip after 1 year. Conclusions: Ibandronate 150 mg by mouth once a month prevents anastrozole induced bone loss and results in significant increases in BMD at the hip and lumbar spine in osteopenic and osteoporotic patients. Analysis of the biochemical markers of bone metabolism is underway and relationships between biochemical and BMD changes will be presented. No significant financial relationships to disclose.