Ratio of lymph node to primary tumor SUV_max multiplied by maximal tumor diameter on positron emission tomography/integrated computed tomography may be a predictor of mediastinal lymph node malignancy in lung cancer

Positron emission tomography/integrated computed tomography (PET/CT) provides the most accurate imaging modality for preoperative lung cancer staging. However, the diagnostic accuracy of maximum standardized uptake value (SUV_max) for mediastinal (N2) lymph nodes (LN) is unclear. We compared SUV_max, the ratio of LN to primary tumor SUV_max (SUV_n/t), and SUV_n/t multiplied by maximal tumor diameter (SUV_index) in terms of their abilities to predict mediastinal LN malignancy. We retrospectively analyzed 170 mediastinal LN stations from 73 consecutive patients who underwent systemic LN resection and PET/CT within 27 days. The SUV_max of the primary tumors was >2.0 and the SUV_max of the mediastinal LN stations ranged from 2.0 to 7.0 on PET/CT. Receiver-operating characteristic curves (ROCs) of SUV_max, SUV_n/t, and SUV_index were calculated separately and the areas under the curves (AUCs) were used to assess the abilities of the parameters to predict LN malignancy. The optimal cutoff values were calculated from each ROC curve and the diagnostic abilities were also compared. The diagnostic accuracies of the 3 methods were also assessed separately in smoking and nonsmoking patients. Twenty-eight LN stations were malignancy-positive and the remaining 142 were malignancy-negative. The AUCs for SUV_index, SUV_n/t, and SUV_max were 0.709, 0.590, and 0.673, respectively, and the optimal cutoff values for SUV_index, SUV_n/t, and SUV_max were 1.11, 0.34, and 3.6, respectively. The differences between SUVindex and SUV_n/t were significant, but there was no significant difference between SUV_index and SUV_max. There were no significant differences between smokers and nonsmokers in the AUCs for any of the methods for predicting LN malignancy (P values >0.05). SUV_index may be a predictor of mediastinal LN malignancy in lung cancer patients.