Hypocalcemia in a Patient With Metastatic Prostate Cancer From Denosumab Treatment

Denosumab is a humanized monoclonal antibody that binds RANKL to inhibit osteoclast activity. It is indicated for the prevention of skeletal-related events (SRE) in patients with solid tumors who have bone metastasis and in patients with multiple myeloma. Hypocalcemia is one of the known side effects of denosumab, which can be prevented with calcium supplementation. We present a case of a 72-year-old male with diagnosed metastatic prostate cancer who had received one dose of denosumab 10 days prior to presentation with fatigue, insomnia, and somnolence. His labs showed severe (Grade 4) hypocalcemia, which improved with intravenous calcium supplementation. This case highlights a known but life-threatening side effect of denosumab and the potential need for prolonged calcium monitoring in patients placed on the drug.