A Study to Evaluate the Efficacy and Safety of Narlumosbart (JMT103) in Patients With Giant Cell Tumor of Bone

Inclusion Criteria: Fully informed and signed informed consent; Male or female adults aged ≥ 18 years or skeletally mature adolescents must weigh at least 45 kg and ≥ 12 years of age; Pathologically confirmed giant cell tumor of bone that is surgically unresectable or for which the planned surgery is associated with functional compromise or morbidity; Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2. Exclusion Criteria: Previous or ongoing osteomyelitis or osteonecrosis of the jaw, non-healed dental/oral surgery, active dental or jaw condition requiring oral surgery, planned invasive dental procedure during the study; Known or suspected diagnosis of other giant cell-rich tumors, brown cell tumor of bone, or Paget's disease; Known diagnosis of malignancy within the past 5 years, except for definitively treated superficial basal cell carcinoma or cervical carcinoma in situ; Bone metabolic disease including hypo-/hyperparathyroidism, hypo-/hyperthyroidism (except for no need treatment subclinical hypothyroidism), hypopituitarism, hyperprolactinemia, Cushing's syndrome, acromegaly, etc.; Active infections requiring systematic treatment within 7 days prior to randomization; Known human immunodeficiency virus (HIV), syphilis infections or viral hepatitis; Current receiving other anti-tumor therapy (such as radiation, chemotherapy, or embolization, etc.); Concurrent bisphosphonate treatment; Use of anti-receptor activator of nuclear factor-κB ligand (RANKL) antibody within six months prior to screening, or no response to previous RANKL antibody treatment; Known allergic/hypersensitive reaction to JMT103, positive control drug, calcium and vitamin D; Pregnant or lactating females; For those of child bearing potential, refusal to use effective contraception methods from signing informed consent to 6 months after last administration.