Imaging gastric cancer with PET and the radiotracers 18F-FLT and 18F-FDG: a comparative analysis. 
In this pilot study, we evaluated 3'-deoxy-3'-(18)F-fluorothymidine (FLT) PET for the detection of gastric cancer and compared the diagnostic accuracy with that of (18)F-FDG PET.  Forty-five patients (31 male and 14 female) with histologically proven locally advanced gastric cancer underwent attenuation-corrected whole-body (18)F-FLT PET and (18)F-FDG PET/CT (low-dose CT). ( 18)F-FLT emission images were acquired on a full-ring PET scanner 45 min after the injection of 270-340 MBq of (18)F-FLT. ( 18)F-FDG PET/CT was performed 60 min after the injection of 300-370 MBq of (18)F-FDG.  Mean standardized uptake values for (18)F-FLT and (18)F-FDG were calculated using circular ROIs (diameter, 1.5 cm) in the primary tumor manifestation site, in a reference segment of the liver, and in the bone marrow and were compared on a lesion-by-lesion basis.  According to the Lauren classification, 15 tumors (33%) were of the intestinal subtype and 30 (67%) of the nonintestinal subtype. ( 18)F-FLT PET images showed high contrast for the primary tumor and proliferating bone marrow.  In all patients (45/45), focal (18)F-FLT uptake could be detected in the primary tumor.  In contrast, 14 primary tumors were negative for (18)F-FDG uptake, with lesional (18)F-FDG uptake lower than or similar to background activity.  The mean standardized uptake value for (18)F-FLT in malignant primaries was 6.0 +/- 2.5 (range, 2.4-12.7).  In the subgroup of (18)F-FDG-positive patients, the mean value for (18)F-FDG was 8.4 +/- 4.1 (range, 3.8/19.0), versus 6.8 +/- 2.6 for (18)F-FLT (Wilcoxon test: P = 0.03).  Comparison of mean (18)F-FLT and (18)F-FDG uptake in tumors with signet ring cells revealed no statistically significant difference between the tracers (6.2 +/- 2.1 for (18)F-FLT vs. 6.4 +/- 2.8 for (18)F-FDG; Wilcoxon test: P = 0.94).  The results of this study indicate that imaging gastric cancer with the proliferation marker (18)F-FLT is feasible. ( 18)F-FLT PET was more sensitive than (18)F-FDG PET, especially in tumors frequently presenting without or with low (18)F-FDG uptake, and may improve early evaluation of response to neoadjuvant treatment.