Long-term effects of anastrozole on bone mineral density: 7-year results from the ATAC trial

Background: This 'Arimidex', Tamoxifen, Alone or in Combination (ATAC) trial sub-study examined the effects of anastrozole and tamoxifen on bone mineral density (BMD) following 5 years of treatment. Patients and methods: Lumbar spine and total hip BMD were assessed at years 6 and 7 in a total of 71 eligible patients. In total, 50 patients had evaluable data. Results: Following anastrozole treatment, the lumbar spine median BMD increased by 2.35% (P = 0.04) and 4.02% (P = 0.0004) at years 6 and 7, while total hip median BMD increased by 0.71% (P = 0.3) and 0.5% (P = 0.8). After tamoxifen treatment, lumbar spine median BMD decreased by 0.79% (P = 0.2) and 0.30% (P = 0.9) at years 6 and 7, while total hip median BMD decreased by 2.09% (P = 0.0003) and 2.52% (P = 0.0002). Patients with a normal BMD or who were osteopenic at 5 years did not become osteoporotic. Conclusions: Anastrozole treatment-related bone loss did not continue into the off-treatment follow-up period. The recovery in lumbar spine BMD and absence of further loss at the hip is consistent with the reduction in the annual rate of fracture observed after treatment cessation in the main ATAC trial.