RESUMO
PURPOSE: The aim of this study is to test the hypothesis that positron emission tomography (PET) with 3'-deoxy-3'-[(18)F]-fluorothymidine ((18)F-FLT) can differentiate malignancy from benign leiomyoma better than PET with 2-deoxy-2-[(18)F]fluoro-D-glucose ((18)F-FDG), and to evaluate whether (18)F-FLT and (18)F-FDG uptake correlate with immunohistochemical index of cell proliferation. METHODS: The protocol of this prospective study was approved by the institutional ethics committee, and all patients gave written informed consent. Fifteen patients (aged 26-65 years, median 44 years) with uterine corpus tumor which has the possibility of being leiomyosarcoma underwent (18)F-FLT and (18)F-FDG PET scans. Maximum standard uptake value (SUV(max)) of PET scans and Ki-67 labeling index of surgical specimens were evaluated. Mann-Whitney's U test was used for comparing uptakes between benign and malignant, and linear regression analysis was used for evaluating the correlation between Ki-67 labeling index and SUV(max). RESULTS: Five cases were diagnosed as malignant (leiomyosarcoma for 3 cases, and carcinoma for 2 cases), and the others were benign leiomyoma. Sensitivity and negative predictive value of both tracers for detecting malignancy was 100%. Specificity, positive predictive value and accuracy of (18)F-FLT PET were higher than those of (18)F-FDG PET. Difference in SUV(max) between malignant and benign was significant for (18)F-FLT PET (P < 0.01), but not for (18)F-FDG PET. While all the malignant cases showed positive uptake in both tracers, a case of leiomyosarcoma with huge necrosis showed relatively low uptake. Uptake of (18)F-FLT showed better correlation with Ki-67 labeling index compared with (18)F-FDG (R(2) = 0.91 vs. R(2) = 0.26). CONCLUSION: Negative findings on additional (18)F-FDG or (18)F-FLT PET may rule out the possibility of malignancy for the patients with suspected leiomyosarcoma diagnosed by conventional methods. (18)F-FLT PET is superior to (18)F-FDG PET in differentiating malignant from benign leiomyoma. Moreover, (18)F-FLT uptake correlated well with the immunohistochemical index of cell proliferation.