Assessment of denosumab treatment effects and imaging response in patients with giant cell tumor of bone 11 Medical and Health Sciences 1103 Clinical Sciences

Background: Denosumab has been shown to reduce tumor size and progression, reform mineralized bone, and increase intralesional bone density in patients with giant cell tumor of bone (GCTB); however, radiologic assessment of tumors in bone is challenging. The study objective was to assess tumor response to denosumab using three different imaging parameters in a prespecified analysis in patients with GCTB from two phase 2 studies. Methods: The studies enrolled adults and adolescents (skeletally mature and at least 12 years of age) with radiographically measurable GCTB that were given denosumab 120 mg every 4 weeks, with additional doses on days 8 and 15 of cycle 1. The proportion of patients with an objective tumor response was assessed using either Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST), European Organisation for Research and Treatment of Cancer response criteria (positron emission tomography [PET] scan criteria), or inverse Choi density/size (ICDS) criteria. Target lesions were measured by computed tomography or magnetic resonance imaging (both studies), PET (study 2 only), or plain film radiograph (study 2 only). Results: Most patients (71.6%) had an objective tumor response by at least one response criteria. Per RECIST, 25.1% of patients had a response; per PET scan criteria, 96.2% had a response; per ICDS, 76.1% had a response. 68.5% had an objective tumor response ≥ 24 weeks. Using any criteria, crude incidence of response ranged from 56% (vertebrae/skull) to 91% (lung/soft tissue), and 98.2% had tumor control ≥ 24 weeks. Reduced PET avidity appeared to be an early sign of response to denosumab treatment. Conclusion: Modified PET scan criteria and ICDS criteria indicate that most patients show responses and higher benefit rates than modified RECIST, and therefore may be useful for early assessment of response to denosumab. Trial registration: ClinicalTrials.gov Clinical Trials Registry NCT00396279 (retrospectively registered November 6, 2006) and NCT00680992 (retrospectively registered May 20, 2008).