Hypercalcemia as a marker of in-hospital mortality and resource utilization in breast cancer: A national analysis.

e12711 Background: Hypercalcemia is a well-recognized oncologic emergency associated with advanced malignancy and poor outcomes. While its clinical impact has been described broadly across solid tumors, contemporary national data characterizing the burden, temporal trends, and outcomes of hypercalcemia specifically among patients hospitalized with breast cancer remain limited. We evaluated national trends in prevalence, in-hospital mortality, and healthcare utilization associated with hypercalcemia among breast cancer hospitalizations in the United States. Methods: We conducted a retrospective, cross-sectional study using the National Inpatient Sample (NIS) from 2016–2020. Adult hospitalizations with a diagnosis of breast cancer were identified using ICD-10-CM codes. Hypercalcemia was defined by ICD-10 code E83.52. Survey-weighted analyses were performed to estimate national prevalence, temporal trends, in-hospital mortality, length of stay (LOS), and total hospital charges. Multivariable survey-weighted logistic regression was used to assess the association between hypercalcemia and in-hospital mortality, adjusting for age and sex. All analyses accounted for the complex sampling design of the NIS. Results: An estimated 166,127 weighted breast cancer hospitalizations were identified from 2016–2020. The weighted prevalence of hypercalcemia among breast cancer admissions increased from 2.57% in 2016 to 3.49% in 2020. Patients with hypercalcemia experienced significantly higher in-hospital mortality compared with those without hypercalcemia, with consistent differences observed across all study years (2020: 9.4% vs 5.0%). After adjustment, hypercalcemia was independently associated with increased odds of in-hospital mortality (adjusted OR 2.01, 95% CI 1.63–2.47). Hypercalcemia was also associated with longer LOS (2020: 7.37 vs 5.12 days) and higher mean hospital charges ($94,852 vs $70,946). Nationally, hypercalcemia accounted for an estimated 5,585 breast cancer hospitalizations annually. Conclusions: Among hospitalized patients with breast cancer, hypercalcemia is increasingly prevalent and independently associated with higher in-hospital mortality and substantial healthcare utilization. Although hypercalcemia likely reflects advanced disease burden and metastatic involvement, these findings highlight its value as a clinically meaningful marker of acute illness severity, identifying a high-risk inpatient population with disproportionate mortality and resource utilization.