Radiographics. 2016 Jan-Feb;36(1):293-4. doi: 10.1148/rg.2016150073.
Flavell RR1, Naeger DM1, Mari Aparici C1, Hawkins RA1, Pampaloni MH1, Behr SC1.
Fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) is commonly performed for staging and restaging of solid tumors. Although most solid tumors demonstrate high uptake of FDG, many others do not. Low FDG uptake may be due to various reasons, including tumors with low glucose metabolism or low cellularity, improper patient preparation, and small tumor size. The presence of low-level FDG uptake could be a source of scan misinterpretation in these low-cellularity or low-glucose-metabolizing tumors, including low-grade lung adenocarcinomas, renal cell cancers, and mucinous neoplasms. The ability to detect lesions at PET/computed tomography (CT) stems from many factors, including size of the lesion, ability of the tumor to concentrate FDG, proper patient preparation, background FDG uptake in surrounding tissues, and type of scanner used. Several examples of low-grade lung adenocarcinoma, renal cell cancer, and mucinous neoplasms are presented that have low FDG uptake. For example, Figure 1 depicts a renal cell cancer without associated FDG avidity above background activity.
In many neoplasms, including hepatocellular carcinoma (HCC), lymphoma, and prostate cancer, there is strong evidence that increasing FDG avidity correlates with poor prognosis and poor response to treatment. In these cases, high FDG uptake likely correlates with dedifferentiation or transformation to a more aggressive form of cancer. For example, in HCC, high FDG uptake predicts poor response to radiation therapy, transarterial chemoembolization, and liver transplantation and is also associated with higher stage and the presence of metastatic disease. Similarly, lesions with high FDG uptake in a patient with a known low-grade lymphoma are suspicious for high-grade transformation (also called Richter transformation). Therefore, in lymphoma, prostate cancer, and HCC, it is important for radiologists to report the degree of FDG uptake.