The Incidence of Bone Metastases and Skeletal-Related Events in Breast Cancer Patients: A Population-Based Cohort Study in Denmark (1999 – 2007).

Abstract

Abstract Background Breast cancer (BrCa) is the most commonly diagnosed cancer among women in the industrialized world. More than half of women presenting with metastatic BrCa develop bone metastases. Bone metastases increase the risk of skeletal-related events (SREs), defined as radiation to bone, pathologic fractures, spinal cord compression, bone surgery, or altered antineoplastic therapy to treat bone pain. Both bone metastases and SREs are associated with unfavorable prognosis and greatly affect quality of life. To date, the epidemiology of the subgroup of BrCa patients who develop bone metastases and/or SREs has not been well-characterized. Our objective was to estimate the one- and five-year incidence of bone metastases and SREs in a large population cohort of newly-diagnosed BrCa patients in Denmark (population ∼ 5.4 million inhabitants). Methods We identified women diagnosed with BrCa (International Classification of Diseases, 10th Revision (ICD-10) code C50.x.) from January 1, 1999 through December 31, 2007, with follow-up through April 2008. We retrieved this data from Denmark's National Registry of Patients (NRP), which includes records from all Danish hospitals. We also identified bone metastases (ICD-10 code C79.5) and recorded SREs. The Kaplan-Meier method was used to estimate time to bone metastases and time to first SRE. We also calculated 1- and 5-year incidence rates (IR) of bone metastases and first SRE in newly-diagnosed BrCa patients. Results We identified 35,941 BrCa patients from the NRP. The median age at diagnosis was 62 years (range, 18-104 years). A total of 1,494 (4%) patients developed bone metastases during follow-up, and of these, 712 developed an SRE. The distribution of SREs by type were 394 (55%) with radiation to the bone, 133 (19%) with pathological or osteoporotic fracture, 42 (6%) with bone surgery, and 143 (20%) with spinal cord compression. The 1-year IR of bone metastases was 13.7 [95% confidence interval (CI): 12.5-15.0] per 1000 person-years (P-Y). The 1-year IR of SREs among patients with bone metastases was 55 times that of the 1-year IR of bone metastases in BrCa patients at 759.2 (95% CI: 662.0-870.5) per 1000 P-Y. After five years of follow-up, the incidence curves plateaued at approximately 4% and 48% for bone metastases and SREs, respectively (Figures 1 and 2). Conclusions Among breast cancer patients with bone metastases, there was a strong tendency towards development of SREs within a year of bone metastases diagnosis; however, this phenomenon stabilized beyond 5 years of bone metastases diagnosis. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 2051.