This prospective observational study is going to figure out the safety and efficacy of denosumab as an post-operative strategy.All the patients enrolled will take denosumab according to the protocols.We focus on the recurrence rate after the drug withdrawl and possibility of malignant transformation.

This prospective observational study is going to figure out the safety and efficacy of denosumab as an post-operative strategy.

This study only included patients who meet all the following criteria: (1) With treatment-naïve sacral giant-cell tumor (GCT) firstly treated in our center (for referral patients, only those with definite diagnosis were included); (2) Being diagnosed with classic giant-cell tumor of bone (GCTB) by puncture pathology prior to treatment (for referral patients, definite diagnosis shall be made by the Pathology Department in our center through pathology consultation on tissue sections); (3) previously denosumab-naïve.

Data collection:The following data of patients included in this study were collected: (1) basic information: age, gender; (2) pathological data: puncture pathological diagnosis, and postoperative pathological findings; (3) the imaging findings (including X-ray, CT, Magnetic resonance(MR), Positron Emission Tomography-Computed Tomography(PET-CT)) and functional assessment of patients in the neoadjuvant denosumab group before and after the use of denosumab; (4) intraoperative blood loss, and duration of operation; (5) imaging findings in postoperative follow-up re-examination and outcome.

functional assessment: For sacral giant cell tumor:The Motor Urination defecation(MUD) scoring system published on Spine by our center in 2016 , which include three domains (motor function and sensation of lower limbs [M], urination and uriesthesia [U], and Defecation and rectal sensation [D]) with three items in each domain (each item can be scored by 0, 1, 2 or 3, and the maximum score is 27), was applied in the functional assessment of sacral nerves.

For GCT occurs in Limbs ,we use Musculoskeletal Tumor Society (MSTS) 93 to record the function.

All the patients enrolled will take denosumab according to the protocols:denosumab 120mg was administrated to patients by subcutaneous injection every four weeks, with loading doses on Day 8 and Day 15 of the first cycle,them take it monthly till 1 year after the surgery.We focus on the recurrence rate after the drug withdrawl and possibility of malignant transformation.

Inclusion Criteria:

(1) With treatment-naïve sacral GCT firstly treated in our center (for referral patients, only those with definite diagnosis were included); (2)single center lesion (3) Being diagnosed with classic GCTB by puncture pathology prior to treatment (for referral patients, definite diagnosis shall be made by the Pathology Department in our center through pathology consultation on tissue sections); (4) previously denosumab-naïve.

Exclusion Criteria:(1)primary malignant giant cell tumor of bone(2)radiation therapy in history(3)lung metastasis at first diagnosis

Patients with giant cell tumor of bone referred to, or being treated at Peking University People's Hostpital.