The occurrence of fractures after adjuvant treatment of breast cancer: a DBCG register study.

BACKGROUND: Adjuvant treatment in breast cancer patients especially with aromatase inhibitors (AIs) has adverse effects on bone metabolism resulting in an increased occurrence of fractures. In order to demonstrate this occurrence, long-term follow-up studies are necessary. From several national registries in Denmark, it is possible to link data from different sources and analyze this issue. METHODS: A study cohort of 68,842 breast cancer patients prospectively diagnosed and registered in the Danish Breast Cancer Cooperative Group's database during the period 1995-2012 formed the basis of the analysis. These data were matched with data on all types of fractures from the Danish National Patient Register and vital data from the Danish Civil Registration System. RESULTS: After data cleaning 66,502 patients were available for analysis and 16,360 of these had incurred 20,341 fractures with 13,182 patients having just one fracture. These fractures were distributed over 214 specific fracture sites. An extended multivariable Cox regression model revealed significant association between the occurrence of fractures and age, menopause, Charlson comorbidity index (CCI) and endocrine therapy such that late menopause and tamoxifen treatment were associated with a lower occurrence and AI treatment, age and CCI were associated with a higher occurrence of fractures. CONCLUSION: Before advising adjuvant therapy with AIs fragile patients with chronic diseases should receive special attention in order to reduce the incidence of fractures in this vulnerable group of patients.