Use of monthly oral ibandronate to prevent anastrozole-induced bone loss during adjuvant treatment for breast cancer: Two-year results from the ARIBON study

Abstract

554 Background: The ARIBON trial is a double-blind, randomized, placebo-controlled study designed to evaluate the impact of bisphosphonate treatment on bone mineral density (BMD) in postmenopausal women taking adjuvant anastrozole for their endocrine responsive breast cancer. Methods: BMD was assessed in 131 patients prior to commencing adjuvant endocrine treatment. 68, 50, and 13 patients were found to be normal (T >-1.0, group 1), osteopenic (T -1.0 to -2.5, group 2), and osteoporotic (T <-2.5, group 3), respectively. All patients were treated with anastrozole 1mg once a day and calcium and vitamin D supplementation. In addition, group 2 patients were randomized on a 1:1 basis to receive either treatment with oral ibandronate 150 mg every month or placebo. Group 3 patients were treated with open label oral ibandronate 150mg every month. BMD and bone marker measurements were repeated at regular intervals for two years. Group 1 patients were followed up on calcium and vitamin D supplements alone. Results: BMD changes in groups 2 and 3 are shown in the table. In group 2 the mean difference in percentage BMD changes between the ibandronate and placebo treated patients after 1 and 2 years was 5.5 and 6.2% (95% CI 2.4–10.0) at the lumbar spine (LS) and 3.2 and 4.5% (95% CI 1.7–7.3) at the hip (TH) (p<0.01, independent samples t test). After 1-year Urinary n-telopeptide (uNTX), serum c-telopeptide (sCTX), and serum bone-specific alkaline phosphatase (sBALP) levels declined in patients receiving ibandronate (21, 26, and 23%, respectively) and increased in those taking placebo (40, 35, and 40%, respectively). Biomarker assessments at 2 years are ongoing. As expected, group 1 patients lost 4.8% (range -13.8, +4.5) at the LS and 3.7% (range -15.9, +1.3) at the TH after 2 years. Conclusions: Ibandronate 150 mg by mouth once a month prevents anastrozole-induced bone loss and results in significant increases in BMD at the LS and TH in osteopenic and osteoporotic patients. Mean Percentage Change in BMD (Ranges) Osteopenia Osteoporosis Ibandronate Placebo Ibandronate 1 yr n=23 2 yr n=21 1 yr n=25 2 yr n=19 1 yr n=12 2 yr n=12 LS +3.11 (-3.8, +15.1) +2.98 (-8.9, +19.9) -2.35 (-10.5, +2.2) -3.22 (-16.0, +4.3) +5.02 (-8.7, +15.2) +3.52 (-4.9, +14.6) TH +0.98 (-4.1, +5.6) +0.60 (-9.0, +6.9) -2.27 (-9.9, +5.2) -3.90 (-12.3, +7.2) +2.90 (-1.0, +8.5) +2.49 (-3.7, +8.1) Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration AstraZeneca Oncology, Roche AstraZeneca Oncology