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.
Methods: 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.
Results: 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).
Conclusion: 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.