In vivo characterization of proliferation for discriminating cancer from pancreatic pseudotumors

We have determined the ability of PET with the thymidine analog 3′-deoxy-3′-¹⁸F-fluorothymidine (FLT) to detect pancreatic cancer and to differentiate malignant from benign pancreatic lesions. Methods: In this prospective study, ¹⁸F-FLT PET was performed on 31 patients with undefined pancreatic lesions. Routine diagnostic procedures included endoscopic ultrasound, MRI, or multislice helical CT of the upper gastrointestinal tract in all patients. Uptake of ¹⁸F-FLT was evaluated semiquantitatively by calculation of mean and maximal standardized uptake values (SUVs). Results were correlated to the reference methods, which were histopathology (23/31) or cytology/clinical follow-up (8/31). Results: All 10 benign pancreatic lesions were negative on ¹⁸F-FLT PET and showed only background activity (specificity, 100%; 90% confidence interval, 74%-100%). On visual interpretation, 15 of 21 malignant tumors presented as focal ¹⁸F-FLT uptake higher than the surrounding background (sensitivity, 71.4%; 90% confidence interval, 52%-89%). ¹⁸F-FLT PET missed 4 well-differentiated and 2 T1 cancers. Mean ¹⁸F-FLT uptake was 3.1 in all malignant tumors (median, 2.8; range, 1.3-8.5), 3.7 in tumors with visual tracer uptake (median, 3.2; range, 2.1-8.5), and significantly higher in malignant than in benign tumors (mean/median, 1.4; range, 1.2-1.7; P < 0.001). For discriminating cancer from benign pancreatic lesions, receiver-operating-characteristic analysis indicated a sensitivity of 81% and specificity of 100% (area under the curve, 0.93) using a mean ¹⁸F-FLT SUV cutoff of 1.8 (maximal ¹⁸F-FLT SUV: area under the curve, 0.92; SUV cutoff, 2.1). Conclusion: In this pilot study, focal uptake of the in vivo proliferation marker ¹⁸F-FLT was detected exclusively in malignant tumors. ¹⁸F-FLT PET may therefore be useful as a diagnostic adjunct for differentiating cancer from benign pancreatic lesions.