Abstract: ¹⁸F-fluorodeoxyglueose (¹⁸F-FDG) is widely used to detect tumor with PET. However, ¹⁸F-FDG is not specific for tumor imaging because glucose is also utilized by other benign cells. 3'-deoxy-3'-¹⁸F-fluorothymi-dine (¹⁸F-FLT) is developed to overcome the limitations of ¹⁸F-FDG and to image cellular proliferation by PET. ¹⁸F-FLTfeatures an excellent proliferation tracerfor PET studies of tumors. The advantage of ¹⁸F-FLT is based on thymidine kinase-1 (TK 1) catalyzed phosphorylation of FLT and the intracellular accumulation of ¹⁸F-FLT is dependent on the presence of TK1, which is closely related to cellular proliferation in tumor cells undergoing DNA replication during the S phase of the cell cycle. Therefore, ISF-FLT is expected to be a feasible PET tracer for diagnosing, evaluating and monitoring the early response to therapy in oncology.