Sequential FDG-PET/CT as a biomarker of response to Sunitinib in metastatic clear cell renal cancer.

Abstract

To test the hypothesis that sequential (18)F-fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) is a correlative marker in metastatic clear cell renal cancer (mRCC), patients were treated with sunitinib. Three sequential scans were conducted to determine whether the timing of the investigation was relevant. Forty-four untreated mRCC patients were enrolled into this prospective phase II study. (18)F-FDG-PET/CT scans were conducted before (n = 44) and after 4 weeks (n = 43) and 16 weeks (n = 40) of sunitinib given at standard doses. The primary endpoint was to correlate FDG-PET/CT response (20% reduction in SUV(max)) at 4 and 16 weeks with overall survival (OS). Forty-three (98%) patients had FDG-PET/CT avid lesions at diagnosis (median SUV(max) = 6.8, range: <2.5-18.4). In multivariate analysis, a high SUV(max) and an increased number of PET-positive lesions correlated with shorter OS [HR: 3.30 (95% CI: 1.36-8.45) and 3.67 (95% CI: 1.43-9.39), respectively]. After 4 weeks of sunitinib, a metabolic response occurred in 24 (57%) patients, but this did not correlate with progression-free survival (HR for responders = 0.87; 95% CI: 0.40-1.99) or OS (HR for responders = 0.80; 95% CI: 0.34-1.85). After 16 weeks of treatment, disease progression on FDG-PET/CT occurred in 28% (n = 12) patients which correlated with a decreased OS and PFS [HR = 5.96 (95% CI: 2.43-19.02) and HR = 12.13 (95% CI: 3.72-46.45), respectively]. Baseline FDG-PET/CT yields prognostic significant data. FDG-PET/CT responses occur in the majority of patients after 4 weeks of therapy; however, it is not until 16 weeks when the results become prognostically significant.