Is there a correlation between tumor proliferative and glycolytic phenotype in high grade soft tissue sarcoma?

Objectives The aim of this study was to compare tumor proliferation - as estimated by FLT (18F-3`-deoxy-3`-fluorothymidine) - with the corresponding tumor glycolytic phenotype - measured by FDG (18F-2’-deoxy-2’-glucose) - in recently diagnosed high grade soft tissue sarcoma (STS) patients using positron emission tomography / computer tomography (PET/CT).

Methods From October 2008 to April 2009, 12 patients (5 men, 7 women; mean age, 62 years [range, 30-94]) with biopsy proven STS underwent 18F-FLT-PET/CT and 18F-FDG-PET/CT imaging before the initiation of neoadjuvant therapy. The patient population included MPNST (n=3), Leiomyosarcoma (n=2), GIST (n=2), NOS (n=2), Liposarcoma (n=1), Angiosarcoma (n=1), and Fibromyxoidsarcoma (n=1). The tumor size and the peak standardized uptake value for FLT (FLT-SUVpeak) and FDG (FDG-SUVpeak) was measured. Linear regression analysis was used to correlate the tumor FDG and FLT uptake.

Results Mean tumor size averaged 9.1±4.2 cm (range, 5.1-18.0 cm). FDG-SUVpeak averaged 7.2±4.3 g/ml (median, 6.1 g/ml; range, 2.8-16.9 g/ml), which was not significantly different compared to the FLT-SUVpeak (mean, 7.0±4.0 g/ml; median, 6.9 g/ml; range, 2.1-16.1 g/ml) (p=0.95). Linear regression analysis indicated no significant correlation between FDG-SUVpeak and FLT-SUVpeak (Pearson Correlation Coefficient, 0.50; p=0.10). FDG uptake was increased in 7 and decreased in 5 patients compared to the FLT uptake.

Conclusions These data suggest that FDG- and FLT-PET imaging are equally well suited to detect and characterize soft tissue sarcomas. However, tumor proliferation as estimated by FLT PET did not correlate with the tumor glycolytic phenotype measured by FDG-PET. The reasons for this finding await further clarification