The effect of anastrozole on bone mineral density during the first 5 years of adjuvant treatment in postmenopausal women with early breast cancer.

Purpose: The administration of aromatase inhibitors is associated with bone loss in postmenopausal women. We assessed changes in bone mineral density (BMD) from baseline to 60 months of treatment in patients receiving anastrozole as initial adjuvant therapy.

Methods: Postmenopausal women with hormone receptor-positive breast cancer receiving anastrozole as adjuvant therapy at our center since 2004 were enrolled in this study. BMD was assessed by dual-energy X-ray absorptiometry at baseline and after 6, 12, 24, 36, 48 and 60 months. Oral bisphosphonate (Bis) treatment was initiated when patients were diagnosed with osteoporosis having a T-score of -2.5 or lower.

Results: Fifty-five patients were enrolled in the study between 2004 and 2011, and the mean follow-up period was 53.6 months. Thirty-five patients were administered Bis (risedronate in 27 patients, alendronate in 8 patients). After 6 months of hormone therapy, BMD decreased by 0.5% from baseline at the lumbar spine (LS) and BMD decreased by 1.5% at the femoral neck (FN). However, BMD increased by 1.9% at the LS and BMD decreased by 1.5% at the FN for 60 months of treatment. In patients treated with upfront Bis (n = 19), 5.4% BMD increase from baseline was noted at the LS whereas in those without Bis (n = 21) BMD decreased by 4.3% from baseline within 24 months (P < 0.0001). Fractures were observed in 4 patients (7.3%), and 1 patient (1.8%) had a fragility fracture.

Conclusions: Upfront treatment of Bis with anastrozole significantly increased BMD at the LS and an optimal use of Bis would not increase bone fractures.

Trial Registration: UMIN0000017571.