Risk Factors, Patterns, and Distribution of Bone Metastases and Skeletal-Related Events in High-Risk Breast Cancer Patients

Background: More than a quarter of breast cancer patients are at risk to develop recurrent metastases to the bone. Objective: This study was designed to identify risk factors and predilections of bone metastasis and skeletal-related events (SRE) in a population of breast cancer survivors initially diagnosed in advanced stages and with high-risks of relapse. Methods: Associated risk factors, distribution, and attainable treatment of bone metastasis and SRE were analyzed in a cohort of 1,329 breast cancer patients. The association with dependent variables was subsequently analyzed using multivariable logistic regression. Sociodemographic and adverse clinical characteristics were included as covariates of progression into bone metastasis and SREs. Results: Of 1329 breast cancer patients, 246 patients (18.5%) were diagnosed as metastatic breast cancer in which 232 of them (94.3%) had bone metastases. Spines were the most common sites of bone metastases (25.6%). In multivariable analysis, advanced stage at diagnosis (OR=1.840, 95%CI:1.198-2.826, P=0.005), luminal subtype (OR=1.788, 95%CI:1.206-2.652, P=0.045), lobular histology (OR=1.795, 95%CI:1.012-3/184, P=0.046), positive axillary lymph node (OR=1.771, 95%CI:1.087-2.886, P=0.022), multiple metabolic comorbidities (OR=2.193, 95%CI:1.371-3.508, P=0.001), early menopause (OR=2.136, 95%CI:1.116-4.464, P=0.046) were significantly associated with risk of recurrent bone metastases. SREs occurred in 89 (68.5%) patients. Several risk factors for SREs were early menopausal age (OR=2.342, P=0.024), advanced stages (OR=1.404, P=0.039), lobular histology (OR=2.279, P=0.007), and having multiple metabolic comorbidities (OR=1.728, P=0.039). Conclusion: Bone metastases and SREs are relatively high in breast cancer patients diagnosed in advanced stages. Luminal subtypes, having multiple metabolic comorbidities, and lobular histology are associated with higher risks of recurrent bone metastases. Living in rural areas and advanced stage at diagnosis as a risk factors for bone metastases might represent a social gradient of care delivery.