摘要Background Pharmacologic options for treatment of osteolytic diseases especially in children are limited.Although not licensed for use,denosumab,a fully humanized antibody to RANKL,is used in children with good effects.Among others,one possible indication are giant cell tumors and aneurysmatic bone cysts.However,there are reports of severe hypercalcemia during weeks to months after termination of denosumab,that are rarely seen in adults.Methods We collected data of four patients,aged 6-17 years,who experienced severe hypercalcemia after completion of treatment with denosumab for unresectable giant cell tumors of bone or aneurysmal bone cysts and methods of their treatment.The detailed case information were described.Results One patient was treated with long-term,high-dose steroid therapy,leading to typical Cushing's syndrome.Another patient was restarted on denosumab repeatedly due to relapses of hypercalcemia after every stop.Finally,in two patients,hypercalcemia ceased definitely after treatment with bisphosphonates.However,several applications were necessary to stabilize calcium levels.Conclusions There is a considerable risk of hypercalcemia as an adverse effect after denosumab treatment in children.Therapeutic and,preferably,preventive strategies are needed.Bisphosphonates seem to be an option for both,but effective proceedings still remain to be established.