Reduced Dose-density of Denosumab for Unresectable GCTB

Inclusion Criteria: * Histologically proven primary or metastatic unresectable GCTB or resectable GCTB but not a candidate for surgery, excluding primary or metastatic GCTB in the jaw. * Evidence of active disease at time of registration based on local investigator's assessment (according to RECIST v1.1) * Age ≥ 18 years old and skeletally mature (ie, radiographic evidence of at least 1 mature long bone (e.g. humerus with closed growth epiphyseal plate) * Patient must have received denosumab before entering this trial: * The duration of treatment with full dose denosumab (120 mg SC ) as per current label must be at least 12 months and patient may have received up to 15 months of denosumab. * And patient must have received at least 12 doses of denosumab 120 mg before entering into this trial. * ECOG/WHO PS 0-2 * Albumin-adjusted serum calcium level ≥ 2.0 mmol/L (8.0 mg/dL) * Representative formalin fixed, paraffin embedded tumor blocks or unstained tissue slides, either from the primary tumor or a metastatic lesion, must be available for histological central review. * Women of child bearing potential (WOCBP) must have a negative serum (or urine) pregnancy test within 7 days prior to the first reduced dose of study treatment. * WOCBP should use adequate birth control measures, as defined by the investigator, during the study treatment period and for at least 5 months after the last treatment cycle. A highly effective method of birth control is defined as a method which results…