(P 56) CHARACTERIZATION OF DENOSUMAB TREATMENT RESPONSE ON MR PERFUSION IN GIANT CELL TUMORS OF BONE

Objective: MR perfusion is useful for characterization of bone tumors, such as giant cell tumor of bone (GCTB). Denosumab is a monoclonal antibody used neo-adjuvantly in GCTB to facilitate surgery; or long term for axial tumors where surgery comes with high morbidity. We assessed changes in time intensity curve (TIC) - derived perfusion features on dynamic contrast-enhanced MR imaging (DCE-MRI) in GCTB during denosumab treatment and evaluated the duration of treatment effects that occur.

Methods: Patients with GCTB who were treated at the Leiden University Medical Center, and underwent MRI before (t=0) and after 3 (t=3), 6 (t=6) or 12 (t=12) months of denosumab treatment (n=24), were retrospectively included. Regions of interest (ROIs) were manually placed on tumor compartments with visually most intense enhancement on DCE-MRI and intensity curves were created. Time-to-enhancement (TTE), wash-in rate (WIR), maximal relative enhancement (MRE), and area-under-the-curve (AUC) were calculated.

Results: Visual assessment of mean TICs showed relatively early and steep enhancement followed by slow wash-out of contrast before start of treatment at t=0. All 24 patients showed denosumab treatment response on MR perfusion and delay in arrival of contrast and reduced enhancement was seen within 3 months of treatment. TTE increased between t=0 and t=3 (p < 0.001). WIR, MRE and AUC decreased between t=0 and t=3 (p < 0.001, p=0.01 and p=0.02, respectively). No significant differences in features were found between t=3 and t=6 or t=6 and t=12. We found no significant perfusion differences in primary versus recurrent, or axial versus appendicular tumors.

Conclusion: MR perfusion significantly changed in GCTB within 3 months of denosumab treatment compared to baseline. No further change occurred at t=6 or t=12 suggesting that maintenance treatment with lower doses may already be indicated after 3 months. In axial tumor cases where long term denosumab is the preferred therapy, monitoring change in tumor characteristics on MR perfusion may aid optimal drug dose titration and intervals, thereby minimizing side effects.