The impact of treatment compliance on fracture risk in women with breast cancer treated with aromatase inhibitors in the United Kingdom.

No study has yet analyzed the impact of compliance with aromatase inhibitor(AI) treatments on fracture risk in a real-world setting in women with breast cancer. In this study, 8732 women with BC treated with AI, 8732 treated with tamoxifen (TAM), and 8732 age-matched women without BC selected from the Disease Analyzer database (IMS Health) were included. The main outcome measure was the impact of compliance with AI treatment on fracture risk. Demographic data included age, body mass index (BMI), and smoking status. Alcohol dependency, dementia, bone density, visual disturbances, diabetes, and use of corticosteroids were also assessed. Kaplan-Meier curves were used to analyze the proportion of patients with fracture over time, and multivariate Cox regression models were performed to assess the adjusted fracture risk. Mean age was 67.3 years. 17.6, 8.7, and 8.8 % of AI, TAM, and non-cancer patients, respectively, were diagnosed with fracture within 5 years after the index date (p < 0.001). The proportion of women receiving AI with fracture increased with treatment compliance, rising from 8.6 % when treatment persisted for less than a year to 18.0 % when it persisted for between 4 and 5 years (p < 0.001). By contrast, the proportion of fractures in women with BC receiving TAM for the same time periods decreased from 13.0 to 7.9 % (p < 0.001). The risk of fracture was higher in women with BC using AI than in the non-cancer group (HR = 3.00; p < 0.0001). Finally, current smoking status, BMI, dementia, and prescription of corticosteroids had significant impacts on fracture risk. Compliance with AI treatment in women with BC is associated with a clear increase in the risk of fracture, which is much higher than previously reported.