Baseline and on Treatment Biodistribution Variability of 18F-FLT Uptake in Patients with Advanced Melanoma: Brief Communication

Purpose This prospective study evaluates the biodistribution of 18F-FLT PET in patients with advanced melanoma before and after treatment with BRAF/MEK inhibitors. Patients and Methods Eighteen BRAF-positive unresectable stage IIIc or IV melanoma patients referred for 18F-FLT PET/CT before (BL) and during (D14) BRAF/MEK inhibition were included. 18F-FLT accumulation in the liver, bone marrow, blood, and muscle was quantified. Results Baseline interpatient 18F-FLT uptake had a coefficient-of-variation between 17.5% and 21.5%. During treatment, liver uptake increased (SUVmeanBL = 4.86 ± 0.98, SUVmeanD14 = 6.31 ± 1.36, P < 0.001) and bone marrow uptake decreased (SUVmeanBL = 7.67 ± 1.65, SUVmeanD14 = 6.78 ± 1.19, P < 0.025). Both changes were unrelated to baseline metabolic tumor volume or tumor response. Conclusions To assess 18F-FLT PET, both liver and bone marrow uptake may be used as normal tissue references at baseline, but 18F-FLT biodistribution significantly changes in longitudinal response studies when treated with BRAF/MEK inhibitors.