Role of preoperative PET-CT in assessing mediastinal and hilar lymph node status in early stage lung cancer.

BACKGROUND Positron emission tomography combined with computed tomography (PET-CT) is important in the assessment and workup of lung cancer staging. However, inconsistencies between clinical image results obtained and pathologic findings of surgical specimens are still very common, particularly in patients with clinical early stage lung cancer. We sought to clarify the role of PET-CT in predicting mediastinal lymph node status preoperatively in clinical early stage lung cancer patients. METHODS The cases were collected retrospectively from January 2008 to February 2009. All patients were good surgical candidates, and clinically early-stage during the pre-op evaluation, which included CT, PET scan, and cardiopulmonary tests. All patients underwent surgery, with complete pathological evaluation of mediastinal lymph node (LNs). The pathological status and PET Standardized uptake value (SUV)(max) of mediastinal LNs were collected to calculate the ROC curve, and to determine the best cut-off value of PET SUV(max). Other cofactors, including sex, tumor size, tumor SUV(max), histology type, and lobar distribution, were analyzed utilizing correlation study, Chi-square test, and t-test for significance. RESULTS A total of 83 patients were enrolled into the study. The majority of the cases were in pathological early stage (Stage I: 67.5%, Stage II: 12%). The cut-off point of mediastinal LN SUV(max) was 1.6 calculated by receiver operating characteristic (ROC) curve (sensitivity: 40%, specificity: 88.7%, negative predictive rate: 95.1%). The hilar LN SUV(max) was found to have a poor correlation to the final pathologic status of hilar nodes with insignificant p value (0.487). Tumor SUV(max) and increased hilar LN uptake (SUV(max) >  2.0) were found to be significantly correlated with the pathologic status of mediastinal LNs. The false positive rates by PET-CT scan in N1 and N2 nodes were 70% and 78%, respectively, primarily due to inflammatory process (as anthracosis the leading cause). CONCLUSION Integrated PET-CT is a useful tool for predicting the negativity of mediastinal LN status pre-operatively in clinically early stage (Stages I and II) lung cancer but may be relatively inaccurate in predicting hilar LN status and largely confounded by false positives caused by inflammatory process.