Severe denosumab-induced hypocalcemia requiring long-term intensified medication in a patient with EGFR-mutant lung cancer and diffuse osteoblastic bone metastases

Lung cancer often causes bone metastasis, and denosumab is administered to bone metastases to prevent bone-related adverse events. One of the important side effects of denosumab is hypocalcemia, but this is generally not a problem, as it is used with calcium supplementation. A 48-year-old non-smoker male was diagnosed with lung adenocarcinoma with EGFR L858R mutation with diffuse bone metastases. Three days after receiving denosumab, the patient developed weakness and numbness in his limbs and was diagnosed with drug-induced hypocalcemia due to denosumab. It takes more than 4 months for treating the hypocalcemia in this case with continuous intravenous infusion of calcium gluconate with oral calcium supplementation for 2 months of hospitalization and subsequent 2 months of outpatient treatment with intermittent intravenous infusion of calcium gluconate three times a week along with oral supplementation. Tartrate-resistant acid phosphatase-5b (TRACP-5b), a marker of bone resorption, was a biomarker for the required amount of calcium in this case. Patients with lung cancer with diffuse osteoblastic bone metastases could develop severe hypocalcemia and require long-term calcium supplementation.