Prevention of Anastrozole-Induced Bone Loss with Monthly Oral Ibandronate during Adjuvant Aromatase Inhibitor Therapy for Breast Cancer

Purpose: The aromatase inhibitor anastrozole is a highly effective well-tolerated treatment for postmenopausal endocrine-responsive breast cancer. However, its use is associated with accelerated bone loss and an increase in fracture risk. 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 women taking anastrozole. Experimental Design: BMD was assessed in 131 postmenopausal, surgically treated women with early breast cancer at two U.K. centers. Of these, 50 patients had osteopenia (T score −1.0 to −2.5) at either the hip or lumbar spine. All patients were treated with anastrozole 1 mg once a day and calcium and vitamin D supplementation. In addition, osteopenic patients were randomized to receive either treatment with ibandronate 150 mg orally every month or placebo. Results: After 2 years, osteopenic patients treated with ibandronate gained +2.98% (range −8.9, +19.9) and +0.60% (range −9.0, +6.9) at the lumbar spine and hip, respectively. Patients treated with placebo, however, lost −3.22% (range −16.0, +4.3) at the lumbar spine and −3.90% (range −12.3, +7.2) at the hip. The differences between the two treatment arms were statistically significant at both sites (P < 0.01). At 12 months, urinary n-telopeptide, serum c-telopeptide, and serum bone–specific alkaline phosphatase levels declined in patients receiving ibandronate (30.9%, 26.3%, and 22.8%, respectively) and increased in those taking placebo (40.3%, 34.9%, and 37.0%, respectively). Conclusions: Monthly oral ibandronate improves bone density and normalizes bone turnover in patients treated with anastrozole.