Is It time to move beyond FDG toward a more specific yet broadly applicable radiotracer such as FAPI? why yes-and why not.

Fluorine-18 fluorodeoxyglucose (18F-FDG) PET/CT remains the most widely used oncologic imaging modality due to its ability to exploit increased glucose metabolism, a fundamental hallmark shared by many malignancies. However, FDG is limited by its lack of specificity, including uptake in inflammatory and benign processes, high physiologic background activity in the brain, required patient preparation such as fasting-which can be challenging in diabetic patients-and relatively long uptake times, as well as the absence of inherent theranostic potential. These limitations have fueled ongoing debate regarding whether it is time to replace FDG with a more specific yet broadly applicable radiotracer, such as fibroblast activation protein inhibitor (FAPI), which has gained substantial attention across multiple research and clinical scenarios. FAPI PET offers low background uptake, relatively rapid imaging protocols, and theranostic potential. Nevertheless, FDG is unlikely to be replaced in the near future, as it reflects a fundamental metabolic feature shared by many cancers, benefits from well-established infrastructure and reader familiarity, offers robust quantitative capabilities, and remains cost-effective. Rather than replacement, FDG and FAPI are be better regarded as complementary, biology-driven imaging tools, particularly given their fundamentally different mechanisms for detecting cancer.