Abstract
BackgroundBreast 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 pathological fractures, spinal cord compression, bone pain requiring palliative radiotherapy, and orthopaedic surgery. Both bone metastases and SREs are associated with unfavorable prognosis and greatly affect quality of life. Few epidemiological data exist on SREs after primary diagnosis of BrCa and subsequent bone metastasis. We therefore estimated the incidence of bone metastases and SREs in newly-diagnosed BrCa patients in Denmark from 1999 through 2007.MethodsWe estimated the overall and annual incidence of bone metastases and SREs in newly-diagnosed breast cancer patients in Denmark from January 1, 1999 to December 31, 2007 using the Danish National Patient Registry (DNPR), which covers all Danish hospitals. We estimated the cumulative incidence of bone metastases and SREs and associated 95% confidence intervals (CI) using the Kaplan-Meier method.ResultsOf the 35,912 BrCa patients, 178 (0.5%) presented with bone metastases at the time of primary breast cancer diagnosis, and of these, 77 (43.2%) developed an SRE during follow up. A total of 1,272 of 35,690 (3.6%) BrCa patients without bone metastases at diagnosis developed bone metastases during a median follow-up time of 3.4 years. Among these patients, 590 (46.4%) subsequently developed an SRE during a median follow-up time of 0.7 years. Incidence rates of bone metastases were highest the first year after the primary BrCa diagnosis, particularly among patients with advanced BrCa at diagnosis. Similarly, incidence rates of a first SRE was highest the first year after first diagnosis of a bone metastasis.ConclusionsThe high incidence of SREs following the first year after first diagnosis of a bone metastasis underscores the need for early BrCa detection and research on effective treatments to delay the onset of SREs.
Highlights
Breast cancer (BrCa) is the most commonly diagnosed cancer among women in the industrialized world
Breast cancer patients We identified all patients in the Danish National Patient Registry (DNPR) with a first primary diagnosis of BrCa recorded between January 1, 1999 and December 31, 2007
In the subset of BrCa patients (1999 through 2006) for whom we had information on primary stage of BrCa at diagnosis (n = 31,761), 13,515 (43%) patients presented with localized disease, 12,452 (39%) presented with regional disease, 1,557 (5%) presented with metastases, and 4,237 (13%) patients had missing stage data
Summary
We conducted this population-based cohort study in Denmark (population ~ 5.4 million inhabitants). Breast cancer patients We identified all patients in the Danish National Patient Registry (DNPR) with a first primary diagnosis of BrCa (i.e., recurrent or relapsed cases were not included) recorded between January 1, 1999 and December 31, 2007 (during this period, there was no formal mammography screening program in Denmark). Skeletal-related events The DNPR was used to identify SREs after BrCa diagnosis, with surgical procedures coded according to the Danish version of the Nordic Classification of Surgical Procedures (NCSP). We calculated the cumulative incidence and incidence rates of SREs among BrCa patients diagnosed with bone metastases and plotted these estimates as a function of time since bone metastasis diagnosis. To evaluate age at BrCa diagnosis as a risk factor for bone metastases, we stratified the analyses according to the following age groups: =60 years, 60-69 years, and 70+ years.
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