e22504 Background: Positive effect of the monoclonal antibody denosumab in cancer treatment has been reported in recent years. Since surgical treatment is considered the main method of treatment for giant-cell tumors of the bone (GCTB), the purpose of our study was to improve treatment outcomes using denosumab. Methods: The study included 10 patients with verified GCTB (5 men, 5 women, mean age 36±3.14 years). Tumors were located in the upper third of the tibia (3 patients), the lower third of the tibia (3), iliac bone (1), heel bone - 1, the lower third of the femur - 1, the lower third of the humerus - 1.Patients received 2 cycles of neoadjuvant denosumab treatment (120 mg subcutaneously once every 4 weeks) with further tumor resection. The bone defect was reconstructed with bone grafting in marginal resections and endoprosthetics in segmental resections. The effect of neoadjuvant therapy was assessed morphologically by optical light microscopy; histological and histochemical methods were used. Results: Neoadjuvant treatment reduced pain syndrome and restored the support ability. X-ray and spiral X-ray CT showed sclerotic sites in the lytic foci. Consolidation of pathological fractures in the tumor area was registered, as well as fibrosis of the tumor focus. The tissue on the sections of removed material appeared dryish and whitish, it replaced the medullary canal. Microscopic examination of tumors revealed areas of extensive sclerosis foci, and a slight lymphohistiocytic infiltration in some cases. Osteoclasts and osteoblasts were absent in the histological preparations. Conclusions: Neoadjuvant denosumab in GCTB with the following surgery has a pronounced positive effect. This was confirmed by the morphological picture of the operative material demonstrating the development of extensive foci of loose and dense fibrous connective tissue with a small amount of lymphohistiocytic elements.