To describe and illustrate the changes on images of giant cell tumors (GCT) of bone after treatment with denosumab.

Giant cell tumor is a locally aggressive benign bone tumor that usually occurs in young adults with closed physes and involves the epiphyseal-metaphyseal region of the long bones. [1] In Europe and the United States, GCTs represent approximately 5% of all primary bone tumors and 21% of all benign bone tumors. [2] The most common sites include the distal femur, proximal tibia, and distal radius. The general prognosis is usually good. However, pulmonary metastases have been cited as the cause of death in 16-25% of...

Radiographically, GCT is characterized by [4,8,10]: Fig. 1 Eccentric meta-epiphyseal lytic lesions which can demonstrate cortical thinning, expansive bone remodeling and even soft tissue extensión. Large lesions and lesions located in small bones can appear in central location. When located in the epiphysis, GCTs generally extend to the articular surface. These lesions can appear aggressive and are often characterized by extensive local bony destruction, cortical breakthrough, and even soft-tissue expansion. The radiographs shows a narrow transition zone without dense peripheral sclerosis (more typical of non-ossifynig...

GCT treated with denosumab are morphologically different in respect with untreated tumors. Progressive calcification of GCT matrix after denosumab treatment may take place producing a low T1 and T2 weighted images. It should be considered as favourable response to denosumab treatment even if there is no substantial reduction in the size of the tumor. Histological response after denosumab can be confusing and sometimes simulate malignant transformation, careful attention by pathologists and radiologists to the history of denosumab administration is crucial to avoid misdiagnosis and to...

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