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

Authors' Affiliations: ¹ Academic Unit of Clinical Oncology, Weston Park Hospital and ² Academic Unit of Bone Metabolism, University of Sheffield, Sheffield, United Kingdom; ³ Cookridge Hospital and ⁴ St. James' University Hospital, Leeds, United Kingdom

Requests for reprints: James Lester, Cancer Research Centre, Weston Park Hospital, Sheffield S10 2SJ, United Kingdom. Phone: 44-114-2265000; Fax: 44-114-2265878; E-mail: j.lester{at}sheffield.ac.uk.

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.