Risk of cancer treatment-related osteoporosis and fractures among women with breast cancer receiving aromatase inhibitors

Abstract

557 Background: Aromatase inhibitors (AIs) are a novel hormonal therapy for 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. Methods: Using medical and pharmacy claims data from over 5 million beneficiaries between 01/01/1998 and 01/31/2005, we identified 12,368 patients with ≥ 2 breast cancer claims in a 6-month period, who also had no bone metastasis and no prior osteoporosis or fracture claims. Patients who received anti-estrogen therapy were also excluded to remove the protective confounding effects. 1,354 patients receiving an AI (anastrozole, exemestane, letrozole) were compared to 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 bone loss endpoints analyzed were osteoporosis (including osteopenia) and clinical fractures. Results: The univariate analysis found that the prevalence of osteoporosis was 8.7% in the AI group vs. 7.1% in the control group, resulting in a statistically significant relative risk of 1.3 (95% CI=1.1–1.6, p=0.01). The prevalence of bone fracture was also statistically significantly elevated in the AI group compared to 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 statistically significantly higher in the AI group than the non-AI group, with 27% (95% CI=4%-55%, p=0.02) and 21% (95% CI=3%-43%, p=0.02) increase in the risk of osteoporosis and fractures, respectively. Conclusions: This retrospective longitudinal analysis of a large cohort of breast cancer patients 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 alleviate bone loss risk are warranted in women receiving AI for breast cancer. [Table: see text]