Abstract
1685
Objectives Despite the approval of newer agents, therapy (rx) in metastatic melanoma (MM) remains largely palliative. FLT PET has demonstrated potential for monitoring response with metabolic ↓ in FLT uptake seen as early as 1 week. In this phase II trial in MM, we evaluated FLT PET for assessing early metabolic response (EMR) to axitinib, a VEGF inhibitor.
Methods MM patients (pts) with measurable disease, 0-1 prior rx regimens received axitinib 5mg po bid. Of planned accrual of 40 pts, the 1st 15 pts had FLT-PET performed pre-rx and at 4 weeks to assess EMR. Contrast CT was done pre-rx and at 8 week intervals for standard RECIST assessments. We report preliminary results on the FLT PET cohort of pts.
Results 14 of 15 patients, with a total of 61 lesions, demonstrated measurable FLT uptake on pre-therapy PET. 12 pts had the week 4 scan performed. The mean pre-rx maximum SUV (by body weight) was 16.8 (range 3.6, 84.0) and mean post-rx SUVmax was 6.9 (2.9, 14.3). Using 30% ↓ as threshold, 9/12 pts completing both studies showed partial metabolic response (PMR) to axitinib and 3 pts had stable metabolic response (SMR). No correlation between RECIST CT response and FLT-PET EMR was found (p=1.0). Pts with PMR had a median progression-free survival (PFS) of 112 days versus 63 days for pts with SMR (p=0.31). There was no significant difference in PFS when stratified at the median metabolic change of -30% (p=0.20). Groups dichotomized by the median pre-rx SUVmax (8.0) did not differ in PFS (p=0.17). Analysis for overall survival has not matured at this time.
Conclusions We did not find a correlation between pre-rx FLT SUVmax or its change at 4 weeks in relation to PFS in this study. The small sample size may have limited power to detect an association that truly exists. Further investigation of FLT-PET as a biomarker of response in melanoma is needed.
Research Support This study was approved and funded by the National Comprehensive Cancer Network from general research support provided by Pfizer.