WE‐C‐BRC‐05: Use of FLT PET Imaging to Assess Tyrosine Kinase Inhibitor (TKI) Treatment Response

Abstract

Background: Sunitinib (SU) is a tyrosine kinase inhibitor (TKI) with activity against VEGFR. During VEGFR TKI withdrawal, increased pain at sites of metastasis has been observed, which we hypothesize is due to the proliferative flare. []‐fluoro‐3′‐deoxy‐3′‐L‐fluorothymidine (FLT) PET imaging was used as a marker of treatment response, to assess the proliferative flare and to investigate perfusion and vascular status of the tumor. Methods: 14 patients with advanced solid malignancies have been enrolled. SU was given at the standard dose of 50 mg for 4 weeks, followed by a 2 week break. 90‐minute dynamic FLT PET/CT scans were obtained at the baseline, week 4, and week 6. 8 patients with adequate follow‐up time were classified in two groups: with clinical benefit (CB; progressive disease (PD)>6 mo) or without clinical benefit (noCB; PD<6 mo). Changes in the peak FLT standardized uptake value (SUVpeak) were calculated. In addition, FLT kinetic analysis was performed to extract perfusion and vasculature status of the tumor. Results: The differences in FLT uptake were significant between the two groups (CB: −20%, noCB: ∼0%). Interestingly, both groups exhibited a significant increase in SUVpeak during SU withdrawal, but with a significantly higher increase in the group without clinical benefit (CB: +20%, noCB: +50%). The kinetic analysis revealed significant differences in the perfusion at week 4 between the groups (CB: ∼0%, noCB: −40%), with no significant differences at the end of the treatment cycle. Conclusions: Change in SUVpeak was associated with the degree of clinical response. Proliferative increase in the target lesions during SU withdrawal was observed, and was higher for patients with poor clinical outcome.Research sponsored in part by Pfizer.