Risk Factors for Hypocalcemia following Treatment with Denosumab in Patients with Bone Metastases from Prostate Cancer

Objective: To evaluate risk factors for Denosumab-induced hypocalcemia in prostate cancer patients with bone metastases. Methods: In this single-arm, open-label, prospective multicenter study, 48 prostate cancer patients with bone metastases received Denosumab (120 mg on day 1) and androgen-deprivation therapy. Serum calcium, albumin, alkaline phosphatase (ALP), and phosphate levels; chronic kidney disease stage; and serum prostate specific antigen and urine N-terminal telopeptide (u-NTx) levels were examined. Patients were divided into 2 groups on the basis of whether or not they developed hypocalcemia at 1 week or 1 month after Denosumab administration. Risk factors for hypocalcemia were determined by univariate and multivariate logistic regression analysis. Results: Nineteen patients (39.6%) demonstrated hypocalcemia at 1 week after Denosumab administration, and 16 (33.3%) were hypocalcemic at 1 month. Patients with hypocalcemia at 1 week had higher baseline serum ALP levels (1283.4 ± 1489.7 [mean ± SD] vs 467.3 ± 655.8, P=0.013) than patients without hypocalcemia. Patients with hypocalcemia at 1 month had higher baseline serum ALP (1455.5 ± 1694.1, P=0.002) and u-NTx levels (190.9 ± 63.9, P=0.013) and more bone metastases (extent of disease grade ≥ 3; 10 patients, 20.8%, P=0.006) at baseline than patients without hypocalcemia. Multivariate logistic regression analysis revealed that baseline u-NTx of >100 nmol bone collagen equivalents/mmol creatinine was a significant independent risk factor for hypocalcemia (odds ratio=12.41, 95% confidence interval=1.059-145.600, P=0.049). Conclusions: Baseline u-NTx level is an independent risk factor for Denosumab-induced hypocalcemia in prostate cancer patients with bone metastases.