Giant cell tumor of bone following denosumab treatment: assessment of tumor response using various imaging modalities

BACKGROUND: Giant cell tumor (GCT) is a nonmalignant neoplasm composed of multinucleated giant and mononuclear stromal cells. This study aimed to compare imaging findings of GCT pre- and post-denosumab treatment, including lesion size, percentage of signal intensity/density change, and time of initial objective tumor response. This will have a great impact on selection of most appropriate imaging technique to accurately measure therapy response and its related complications, which would influence the physicians to tailor the treatment regimen to suit each patient. RESULTS: As per inverse Choi density/size (ICDS), 16 patients (84.2%) had an objective tumor response and 15 (78.9%) had an increase in density or decrease in signal intensity, and the mean of signal intensity decrease in the treated lesions was 32.4% (95% CI, 18–46.7). Only seven patients (36.8%) had tumors demonstrating ≥ 10% decrease in size, all of which showed a positive change in signal/density except for one. Moreover, 17 patients (89.4%) showed a clear demarcation/low signal intensity margin surrounding ≥ two third of the lesion periphery. The median time to first objective tumor response was approximately 23 weeks. CONCLUSION: Based on the ICDS criteria, most patients with giant cell tumor of bone show objective tumor response to denosumab. Modification of ICDS to include marginal sclerosis or clear demarcation of the lesions might be considered as a separate response criterion to accurately assess the treatment response in patients with GCT.