Survival associated with bone metastases and skeletal-related events in breast cancer patients: A population-based cohort study in Denmark (1999 - 2007)

Abstract

e22210 Background: Breast cancer (BrCa) is the most commonly diagnosed cancer for women in the industrialized world. Among women who present with metastatic BrCa, more than half will develop bone metastases. Bone metastases increase the risk for skeletal-related events (SREs) defined as radiation to bone, pathologic fractures, spinal cord compression, surgery to bone, or change in antineoplastic therapy to treat bone pain. These complications are associated with an unfavorable prognosis and have a major impact on patients' quality of life. However, data on survival of BrCa patients who experience SREs are lacking. We evaluated survival among BrCa patients without bone metastases, with bone metastases, and with both bone metastases and SREs. Methods: Using Denmark's National Registry of Patients (NRP) database, we conducted a retrospective cohort study in the North and Mid- Jutland Region. Patients with a diagnosis of BrCa from January 1, 1999 through December 31, 2007 were identified using the International Classification of Diseases, 10th Revision (ICD-10) codes C50.x. SREs after BrCa diagnosis were identified using the ICD-10 code C79.5. Cox proportional-hazards regression was used to estimate the mortality rate ratio (MRR), adjusting for age and comorbidity, to compare survival among three subgroups of BrCa patients: no bone metastases, bone metastases, and bone metastases with SREs. Results: We identified 9,474 BrCa patients from the NRP. Of these, 621 (7%) developed bone metastases and 267 (3%) developed both bone metastases and SREs during the study period. The 5-year mortality rates among BrCa patients without bone metastases, with bone metastases, and with bone metastases and SREs were 50.7 per 1,000 person-years (PYs), 469 per 1,000 PYs, and 712 per 1,000 PYs, respectively. Compared to BrCa patients without bone metastases, the adjusted MRRs among BrCa patients with bone metastases and patients with bone metastases and SREs were 11.6 [95% confidence interval (CI): 10.9 - 13.6] and 18.1 (95% CI: 15.5 - 21.0), respectively. Conclusions: Our results suggest that bone metastases and SREs have a major impact on the overall mortality of BrCa patients in Denmark. [Table: see text]