Risk of Cancer Treatment—Associated Bone Loss and Fractures Among Women with Breast Cancer Receiving Aromatase Inhibitors

Abstract

Background Aromatase inhibitors (AIs) are a novel hormonal therapy for patients with breast cancer. However, AIs can cause bone loss by blocking estrogen production. This study aims to assess the association between AIs and treatment-related bone loss in a large managed-care population of women with breast cancer. Patients and Methods With use of medical and pharmacy claims, data from > 5 million beneficiaries between January 1, 1998, and January 31, 2005, we identified 12,368 patients with ≥ 2 breast cancer claims in a 6-month period who also had no bone metastases and no previous osteoporosis or fracture claims. Patients who had received antiestrogen (eg, tamoxifen) therapy were also excluded. One thousand three hundred fifty-four patients receiving an AI (anastrozole, exemestane, or letrozole) were compared with 11,014 controls who did not receive an AI with respect to their risk of bone loss. The observation start date for the AI and control groups was defined as the service date of the first AI claim and breast cancer claim, respectively. The endpoints include (1) bone loss, consisting of osteoporosis or osteopenia, and (2) clinical fractures. Results The univariate analysis found that the prevalence of bone loss was 8.7% in the AI group versus 7.1% in the control group, resulting in a significant relative risk of 1.3 (95% confidence interval [CI], 1.1-1.6; P = 0.01). The prevalence of bone fracture was also significantly increased in the AI group compared with the controls (13.5% vs. 10.3%) with a relative risk of 1.4 (95% CI, 1.2-1.6, P = 0.001). Multivariate Cox proportional hazards regressions showed that after adjusting for age and comorbidities, the risk of bone loss remained significantly higher in the AI group than in the non-AI group, with a 27% (95% CI, 4%-55%; P = 0.02) and 21% (95% CI, 3%-43%; P = 0.02) increase in the risk of bone loss and fractures, respectively. Conclusion This retrospective longitudinal analysis of a large cohort of patients with breast cancer corroborates previous findings from smaller clinical trials and demonstrates that AI therapies carry an increased risk of bone loss. Monitoring and treatment management strategies to reduce bone loss risk are warranted in women receiving an AI for breast cancer.