What is the role of PET scanning in the workup of secondary lung tumors?

Updated: Feb 08, 2019
  • Author: Daniel S Schwartz, MD, MBA, FACS; Chief Editor: John Geibel, MD, DSc, MSc, AGAF  more...
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Answer

PET is a physiologic imaging modality that is fundamentally based on the detection of positrons emitted by isotopes of atoms with low atomic weights. Fluorodeoxyglucose (FDG), a D-glucose analogue, is the compound most commonly used for PET. It is a D-glucose labeled with positron-emitting fluorine-18 (18F). Cells take up and phosphorylate FDG as if it were glucose. However, FDG is not metabolized further and tends to accumulate intracellularly. [13]

In general, malignant cells have a higher rate of glucose metabolism than normal cells do. Thus, the intracellular accumulation of FDG, coupled with the preferential accumulation of glucose or its analogue in malignant cells, leads to the visualization of malignancies on PET.

PET is currently used as a diagnostic and staging tool in cancer. In particular, PET is being applied to staging lung cancer. [14]  This modality has a high likelihood of assessing the malignant potential in a pulmonary nodule, particularly if the nodule is solid and larger than 1 cm in diameter. A standard uptake value of greater than 3 is sensitive and specific for cancer. [15]

Limitations of PET include an inability to detect brain metastases, false-negative results in diabetic patients and in patients with malignant lung nodules less than 1 cm in diameter (size has not been shown to play a role in the detection of mediastinal lymph node metastases), and false-positive results in persons with granulomatous or inflammatory diseases. Cost remains an important consideration in ordering this test.

Metabolic imaging of the lungs, such as with PET, is now widely used in clinical practice. The ultimate aim of various advances in lung cancer imaging is to enable clinicians to distinguish between malignant and nonmalignant lesions without the need for tissue sampling. This goal has not yet been achieved. However, these newer imaging modalities play an increasingly important role in clinical decision-making algorithms, research, and drug development. [14, 15, 16]


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