A 25-year-old woman undergoing PET-CT for lymphoma staging receives FDG (fluorodeoxyglucose). FDG uptake in metabolically active tumor tissue occurs because:
- A FDG is transported into cells and phosphorylated but cannot be metabolized further, accumulating as FDG-6-phosphate ✓
- B FDG is preferentially bound by tumor cell surface receptors
- C FDG is retained in cells due to its large molecular size preventing diffusion
- D FDG is metabolized to carbon dioxide and water more rapidly in tumor cells
Correct answer: A. FDG is transported into cells and phosphorylated but cannot be metabolized further, accumulating as FDG-6-phosphate
Explanation
FDG is a glucose analogue that enters cells via GLUT transporters (upregulated in metabolically active tumor cells exploiting the Warburg effect) and is phosphorylated by hexokinase to FDG-6-phosphate. Unlike glucose-6-phosphate, FDG-6-phosphate cannot undergo further glycolysis because the 2'-hydroxyl group required for the next enzymatic step is replaced by fluorine; it therefore accumulates intracellularly. This metabolic trapping mechanism is the basis of tumor imaging with PET. Brain and myocardium also show high normal FDG uptake due to their glucose dependence.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.