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Objective: The aim was to evaluate whether 18F-FLT or 18F-FDG can be used complementaily in predicting the potential of metastasis and recurrence in colorectal cancer (CRC).Methods: Human CRC cell lines SW480 and SW620 were cultured and implanted into nude mice to create the CRC metastasis models.Recurrence of SW480 and SW620 tumor were constructed in nude mice by irradiation.Tumor growth, metastasis and recurrence status were observed.18F-FLT or 18F-FDG small animal PET scan of SW480 and SW620 tumor-bearing mice were obtained before and after irradiation 20Gy.ROI (region of interest) was drawn over tumor and background to calculate T/NT (tumor/non-tumor) using ImageJ software on reconstructed images.Tumor markers, Integrinβ3, HSP27, VEGFR2, and Ki67 were detected by Western-blot and Immunohischemistry.The relation between uptake of the tracers, metastasis capability, recurrence time, and tumor marker expression were evaluated using linear regression.Results: The growth of SW480 tumors was much faster than SW620 (t=3.332, P=0.004).Higher incidence of lung and liver metastases was noted in SW480 than SW620 (P=0.023) tumor-bearing mice.T/NT of 18F-FDG in SW480 or SW620 tumors was different without significantly (2.69±0.98 vs 3.09±1.26, P=0.524).But the T/NT of 18F-FLT between SW480 and SW620 differed significantly (3.65±0.51 vs 2.22±0.42, P<0.001).Integrinβ3, HSP27 expression was higher, while VEGFR2 and Ki67 expression lower, in SW480 than SW620.The capability of metastasis in lung and liver was significantly correlated with 18F-FLT uptake (r=0.574, P=O.006),HSP27 (r=0.894, P=0.008), and Integrinβ3 expression (r=0.635, P=0.088).No correlation was found between 18F-FDG uptake and metastasis (r=-0.129, P=0.330).There was a closely negative correlation between 18F-FDG uptake and recurrence time (r=-0.801, P=0.028).Significant negative correlation also existed between Ki67, VEGFR2 expression and recurrence time (r=-0.864, P=0.013 & r=-0.844, P=0.017).Conclusions: 18F-FLT is more suitable to reflect higher metastatic potential, while 18F-FDG is more suitable to predict recurrence of CRC in mic.18F-FDG and 18F-FLT PET imaging together would be helpful in better predicting biologic behavior of CRC.