Development of the positron emission tomography (PET) diagnostic radiopharmaceutical (¹⁸F) fluoro-2-deoxy-D-glucose (¹⁸F-FDG) subsequently facilitated the discovery and clinical evaluation of several new tracers as imaging markers for cancer. While ¹⁸F-FDG is a widely employed marker forenhanced intracellular glycolysis and metabolic function, one of the newer tracers, (¹⁸F)-3'-fluoro-3'deoxythymidine (¹⁸F-FLT), has been developed as a biomarker for cell proliferation. In this review, the potential of ¹⁸F-FLT as a biomarker for cancer imaging is discussed.