FDG-PET in Mediastinal Nodal Staging of Non-small Cell Lung Cancer: Correlation of False Results with Histopathologic Finding.

Hee Jong Baek, Jin Haeng Chung, Jong Ho Park, Jae Ill Zo, Gi Jeong Cheon, Chang Woon Choi, Sang Moo Lim, Soo Yong Choi, Jong Myeon Hong, Jang Soo Hong

Mediastinal staging of non-small cell lung cancer can be markedly improved by FDG-PET scan, but the problem of false staging of mediastinal nodes by PET scan in non-small cell lung cancer has not yet been overcome. The aim of this study was to identify the mechanism underlying the false staging of mediastinal nodes by FDG-PET in the case of non-small cell lung cancer. To evaluate the factors determining the FDG uptake in mediastinal nodes, FDG-PET was performed preoperatively, and mediastinal dissection with pulmonary resection was performed in 62 patients with NSCLC. GLUT-1 expression was studied by immunohistochemistry of the mediastinal nodes (n=111, true positive <TP> 31, true negative <TN> 41, false positive <FP> 27, false negative <FN> 12) using the anti-GLUT-1 antibody. The size, percentage of tumor (tumor ratio), labeling index (rate of stained tumor), staining intensity of the tumor, level of follicular hyperplasia, and staining intensity of the follicle center in the mediastinal node were also studied. There was no significant difference in size among the 4 nodal groups (TP, TN, FP, FN), nor in the tumor ratio of the metastatic nodes between the TP and FN groups. The labeling index and staining intensity of the TP group were higher than those of the FN group (Mann-Whitney test, p=.001, p=.007) in the case of the metastatic nodes. The level of follicular hyperplasia of the FP group was higher than that of the TN group in the case of the non-metastatic nodes (p=.000). These results suggest that in mediastinal staging of non-small cell lung cancer by FDG-PET, the FN node is associated with low uptake of FDG due to low expression of GLUT-1, and that the FP node is associated with a high level of follicular hyperplasia as a result of there being a reactive change to an inflammatory and/or immune reaction. This is the first report on the mechanism underlying the false results that are sometimes obtained, and which constitute a major problem in the clinical application of FDG-PET to the mediastinal staging of non-small cell lung cancer.