Severe and prolonged hypocalcemia after a single dose of denosumab for metastatic breast cancer with diffuse bone involvement without prior calcium/vitamin D supplementations.

INTRODUCTION

Denosumab is a human monoclonal antibody antiresorptive agent used for the treatment of bone metastasis in different cancer types, including breast cancer. Hypocalcemia is a known adverse effect of denosumab, and early supplementation plays an important role in the prevention and management of hypocalcemia.

CASE REPORT

A 63-year-old female with stage IV estrogen receptor-positive breast cancer with diffuse bone metastasis experienced severe, prolonged hypocalcemia following a single dose of denosumab. The patient also had several risk factors for denosumab-associated hypocalcemia. Despite not receiving additional doses of denosumab, the patient required multiple hospitalizations and outpatient infusions of calcium to resolve her symptomatic hypocalcemia.Management and outcome: Severe hypocalcemia associated with denosumab can be prevented or mitigated by recognizing the risk factors for hypocalcemia and supplementing with vitamin D/calcium. Proposed risk factors include poor renal function, hypoparathyroidism, insufficient calcium intake, and diffuse metastatic bone disease. Studies suggest that early supplementation before starting denosumab can lower this risk.

DISCUSSION

Several cases of severe hypocalcemia associated with denosumab have been reported. However, to the authors' knowledge, this is the first report that highlights the importance of early vitamin D/calcium supplementations for a patient with diffuse metastatic bone disease with pre-existing low levels of calcium.