A RANKL Wrinkle: Denosumab-Induced Hypocalcemia

Area of Science:

• Oncology
• Endocrinology
• Pharmacology

Background:

• Denosumab is a monoclonal antibody targeting RANKL, used to prevent skeletal-related events in bone metastases and osteoporosis.
• RANKL upregulation by tumor cells contributes to bone resorption, making denosumab a crucial therapeutic agent.
• Skeletal-related events (SREs) significantly impact patient quality of life and prognosis in metastatic bone disease.

Observation:

• A 66-year-old male cancer patient developed severe hypocalcemia (total calcium 5.2 mg/dL) 16 days after receiving denosumab.
• Symptoms included fatigue, weakness, and muscle spasms, indicative of electrolyte imbalance.
• Laboratory findings revealed concurrent hypomagnesemia (0.7 mg/dL), a common comorbidity with hypocalcemia.

Findings:

• The patient required intensive intravenous and oral calcium, magnesium, and vitamin D supplementation.
• Post-discharge, serum calcium levels remained unstable, necessitating frequent adjustments to oral supplementation.
• This case underscores the potential for severe and prolonged hypocalcemia as a toxicity of denosumab therapy.

Implications:

• Denosumab's efficacy in reducing SREs must be balanced against the risk of significant hypocalcemia.
• Management of denosumab-induced hypocalcemia requires aggressive and sustained calcium and vitamin D repletion.
• Close monitoring of calcium and magnesium levels is critical during and after denosumab treatment, especially in patients with multiple comorbidities.