Serum Calcium as a Preoperative Surrogate of Tumor Burden in Stage III Breast Carcinoma: A Cross-Sectional Surgical-Oncology Study

Abstract

Background: Stage III breast carcinoma dominates surgical oncology in Indonesian referral hospitals. Tumor-secreted parathyroid hormone-related protein and dysregulated calcium signaling link tumor mass to systemic calcium, yet serum calcium is rarely quantified as a preoperative marker of tumor burden.

Objective: To compare preoperative serum calcium between tumors ≤5 cm and >5 cm and assess its discrimination.

Methods: This cross-sectional study measured preoperative serum calcium in 35 women with Stage III breast carcinoma at Dr. Mohammad Hoesin Central General Hospital, Palembang; tumor size was dichotomized at 5 cm. Analyses used Mann–Whitney U, Spearman correlation, receiver operating characteristic analysis and multivariable logistic regression, with effect sizes and 95% confidence intervals (CI).

Results: Twenty-seven of 35 patients (77.1%) had tumors >5 cm; mean serum calcium was 9.34 ± 0.82 mg/dL. Calcium was higher with tumors >5 cm (9.58 ± 0.76 mg/dL; 95% CI 9.28–9.88) than ≤5 cm (8.54 ± 0.37 mg/dL; 95% CI 8.23–8.85), by 1.04 mg/dL (95% CI 0.66–1.43; Cohen's d = 1.50; U = 0; p < 0.001; r = 0.72). It correlated with size category (Spearman ρ = 0.731; p < 0.001), and no value overlapped between groups (area under the curve 1.000; cut-off 8.95 mg/dL). Calcium was not modeled; immunohistochemical subtype was the only independent predictor (adjusted odds ratio 71.37; 95% CI 2.95–1728; p = 0.009).

Conclusion: In Stage III breast carcinoma, preoperative serum calcium was higher with tumors >5 cm than with smaller tumors; it may be a cheap candidate marker of tumor burden for risk stratification in resource-limited centers, pending validation.