Background: Skeletal-related events (SREs) are significant contributors to the morbidity and mortality in patients with bone metastasis from breast cancer. Thus, bone-modifying agents (BMAs) are recommended in this population. However, the baseline risk factors of SREs in patients with bone metastasis from breast cancer receiving BMAs are not well understood.
Methods: We analyzed the patient-level data from a controlled arm of a clinical trial comparing denosumab with zoledronate in patients with bone metastases from breast cancer (ClinicalTrial.gov ID: NCT00321464) available at Project Data Sphere, a broad-access research platform that collects and curates patient-level data from completed, phase III cancer trials. The primary endpoint was the first SRE after the inclusion to the trial. The time to the first on study SRE was analyzed using Cox proportional hazards model based on patients' baseline characteristics including age, race, ECOG performance status (PS), histology and immunohistochemistry of breast cancer, and urine and serum laboratory data.
Results: Among 756 patients in the zoledronate arm of the trial, we excluded 64 patients with a documented history of osteopenia or osteoporosis. The median age of the patients was 56 years old, the median follow-up was 553 days, and 249 patients (36%) had SREs. The univariate analysis showed that black or African American heritage, ECOG PS > 0, human epidermal growth factor receptor 2 (HER2) positivity, high urine N-telopeptide cross-links / creatinine ratio (NTx/Cre), and elevated serum alkaline phosphatase (ALP) are significant baseline risk factors for SREs. Patients with the characteristics of ECOG PS > 0, HER2 positivity, and elevated ALP also showed a significantly higher hazard ratio of SREs in multivariate analysis.
Conclusions: We determined risk factors for SREs in patients with bone metastasis from breast cancer.
Keywords: Bone metastasis; Breast cancer; HER2; Race; Skeletal-related event.