What is the role of PET scans in the N classification of lung cancer staging?

Updated: Jan 28, 2019
  • Author: Omar Lababede, MD; Chief Editor: Eugene C Lin, MD  more...
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Unlike CT scanning, PET scanning does not rely on the anatomic assessment of nodes. It is primarily a metabolic imaging technique that relies on a biochemical difference between normal and neoplastic cells. Mediastinal nodes containing tumor have an increased uptake of FDG, a glucose analogue labeled with a positron emitter (fluorine-18 [18 F]).

The combined PET/CT is more accurate in the tumor and node staging than that of conventional visual correlation of PET and CT scanning. [26] PET scanning is superior to CT scanning in the assessment of mediastinal and hilar nodal metastases. A large number of studies have validated the higher sensitivity and accuracy of FDG PET/CT compared with conventional CT in detecting metastatic nodal involvement. A meta-analysis compared the diagnostic performance of PET demonstration of mediastinal nodal metastases in patients with non–small cell lung cancer with that of CT (based on 14 studies of the first modalities and 29 the studies of the second). [27] In this study, the mean sensitivity and specificity were 79% and 91%, respectively, for PET and 60% and 77%, respectively, for CT.

False-negative PET CT can be seen with microscopic metastatic nodal involvement and false-positive PET/CT is commonly present with inflammatory reactive nodes. PET/CT can provide valuable information for the assessment of nodal stations that are inaccessible by mediastinoscopy. FDG-PET enables accurate staging of regional lymph node disease in patients with stage I non–small cell lung cancer. A negative PET scan in these patients suggests that mediastinoscopy is unnecessary and that thoracotomy may be performed. FDG-PET is justified as a supporting staging measure in cases presenting unclear differentiation between N2 and N3 after conventional staging.

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