Purpose: To characterize proliferative changes in tumors during the sunitinib malate exposure/withdrawal using 3'-Deoxy-3'-[18F]fluorothymidine (FLT) PET/CT imaging. Patients and Methods: Patients with advanced solid malignancies and no prior anti-VEGF exposure were enrolled. All patients had metastatic lesions amenable to FLT PET/CT imaging. Sunitinib was initiated at the standard dose of 50 mg PO daily either on a 4/2 or 2/1 schedule. FLT PET/CT scans were obtained at baseline, during sunitinib exposure, and after sunitinib withdrawal within cycle #1 of therapy. VEGF levels and sunitinib pharmacokinetic data were assessed at the same time points. Results: 16 patients (8 pts on 4/2 schedule; 8 pts on 2/1 schedule) completed all three planned FLT PET/CT scans, and were evaluable for pharmacodynamic imaging evaluation. During sunitinib withdrawal (change from scan 2 to 3), median FLT PET SUVmean increased +15% (range -14% to +277%) (p=0.047) for the 4/2 schedule and +19% (range -5.3% to +200%) (p=0.047) for the 2/1 schedule. Sunitinib PK and VEGF ligand levels increased during sunitinib exposure, and returned towards baseline during the treatment withdrawal. Conclusions: The increase of cellular proliferation during sunitinib withdrawal in patients with renal cell carcinoma and other solid malignancies is consistent with a VEGFR TKI withdrawal flare. Univariate and multivariate analysis suggest that plasma VEGF is associated with this flare, with an exploratory analysis implying that patients who experience less clinical benefit have a larger withdrawal flare. This might suggest that patients with a robust compensatory response to VEGFR TKI therapy experience early "angiogenic escape".
- Received June 29, 2011.
- Revision received October 7, 2011.
- Accepted October 12, 2011.
- Copyright © 2011, American Association for Cancer Research.