G6P-phosphatase (G6Pase) is a complex of multiple proteins anchored to the ER lumen whose expression has been mostly characterized in the liver, kidney and gut; FDG6P is a recognized substrate for this enzyme, and its activity explains the relatively low sensitivity of 18F-FDG PET/CT in hepatocellular carcinoma [34, 35]. The gene discussed is G6PC1; the disease is hepatocellular carcinoma.