Update of the recommendations for the management and treatment of giant cell bone tumors, on behalf of GroupOS

Introduction: Giant cell tumours (GCTs) are benign primary bone tumours that frequently present with local recurrence and occasionally malignant transformation to high-grade sarcoma. Surgery is the mainstay of treatment and generally consists of intralesional curettage. Denosumab was approved by the European Medicines Agency (EMA) in 2014 for the treatment of skeletally mature adults and adolescents with unresectable GCTs or where resection is likely to result in severe morbidity. Methods: On the basis of national recommendations established in 2016 and a summary of the current state of knowledge, a GroupOS working group was set up to update and develop recommendations on the management and treatment of GCTs in adults, as well as on the place of denosumab. Results: Seven recommendations are proposed here: (1) diagnostic approach and imaging work-up; (2) principles of treatment for GCTs of the limbs; (3) indications for denosumab in GCTs of the limbs; (4) specific features of GCTs of axial location and multifocal GCTs; (5) therapeutic strategy following progression after treatment with denosumab; (6) progression under treatment with denosumab and suspicion of malignant form of GCT under denosumab; (7) monitoring procedures. Conclusion: There are still unresolved issues, such as the optimal duration of treatment or the precise interval between maintenance doses of denosumab. Rarely, GCTs undergo malignant transformation. No clinical, histological or radiographic criteria can accurately predict subsequent aggressive behaviour.