Bone Mineral Density at the Time of Initiating Aromatase Inhibitor Therapy Is Associated With Decreased Fractures in Women With Breast Cancer

Women with estrogen receptor-positive breast cancer who receive an aromatase inhibitor (AI) are at risk for fractures. We aim to determine if dual-energy X-ray absorptiometry (DXA) scans made at the time of AI initiation are associated with decreased fractures. We retrospectively identified 25,158 women with local or regional breast cancer diagnosed between 2005 and 2013 who received AI therapy between 2007 and 2013 from the Medicare-linked Surveillance, Epidemiology, and End Results Program and Texas Cancer Registry databases. We defined baseline DXA screening using claims made between 1 year before and 6 months after each patient's first AI claim to examine determinants of baseline screening using a multivariable GENMOD model. We included a propensity score adjustment in Cox proportional hazard models to assess the association between time-varying DXA screening and the risk of fractures. Additionally, we compared the use of antiresorptive therapy drugs between the two groups. Of the study cohort, 14,738 (58.6%) received DXA screening. The screening rates increased annually from 52.1% in 2007 to 61.7% in 2013. Higher screening rates were observed in patients with younger age, married status, non-Hispanic white race, localized disease, fewer comorbidities, more than one type of aromatase inhibitor drug claim, no state buy-in (surrogate for low socioeconomic status), higher education level, and prior osteoporosis diagnosis. Baseline DXA screening was associated with decreased risk of subsequent fractures (hazard ratio = 0.91; 95% confidence interval, 0.86–0.97, p <.001) after multivariable and propensity score adjustment. Bone-modifying drugs were prescribed to 4440 (30.1%) patients with screening compared with 1766 (16.9%) without (p <.001). Of the 4440 patients who received treatment, 95% received bisphosphonates. Our study demonstrated baseline DXA screening was associated with a decreased risk of fractures and a higher likelihood of receiving antiresorptive therapies. Improvement of the baseline DXA screening is still needed in practice.