FDG-PET/CT in single pulmonary nodule (SPN): preliminary analysis from The Italian Tailored Assessment of Lung Indeterminate Accidental Nodule (ITALIAN) multicentre trial

Objectives: In clinical practice, current guidelines recommend FDG-PET/CT: 1) to characterize SPN in patients with low to moderate pretest probability of malignancy and 2) for staging patients in whom malignancy is strongly suspected or confirmed. The aim of this study was to assess the performance of FDG-PET/CT considering categorical and continuous FDG uptake, for both intra and extra-thoracic disease. We also evaluated the relationship between clinical, demographical or morphological variables with abnormal FDG activity.

Methods: We retrospectively selected 225 consecutive patients (age:67±13 years), without cancer history investigated by FDG-PET/CT for characterization of SPN. According to clinical and instrumental pre-test probability of malignancy (Brock model), patients were stratified in low, intermediate and high malignancy risk categories. FDG uptake in SPN was assessed by a 4-point scoring system and by semi-quantitative analysis of the lung nodule (SUVmax) and in the blood pool (BP) and in the liver (L) (SUVmean). Histopathological and/or follow-up data were used as standard of reference. Diagnostic accuracy of FDG PET/CT in the characterization of SPN was assessed by standard methods. Cut-off values for continuous variables were calculated by ROC analysis. Logistic regression analysis was used to determine the predictors of abnormal FDG uptake.

Results: Histology was available in 164 and follow-up data in 61 patients. SPN was malignant in 111 patients and benign in 114. In all 225 patients considering categorical data analysis (FDG uptake 蠅2 vs. <2), sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of PET/CT for the characterization of SPN were 79%, 75%,75%, 79% and 77%, respectively. Sensitivity and PPV were higher in patients with intermediate and high-risk, while specificity and NPV were higher in low risk category. The cut-offs for better discriminating between benign and malignant lung nodules were 1.60 (81% for both sensitivity and specificity) for SUVmax/SUVmeanBP ratio and 1.21 (81% sensitivity and 80% specificity) for SUVmax/SUVmeanL ratio. In patients at intermediate and high risk of malignancy, by including the SUVmax/SUVmean BP ratio, the specificity shift from 71% to 80% and from 64% to 89%, respectively. In all 225 patients, SUVmax/SUVmeanBP and SUVmax/SUVmeanL ratios were significantly higher in patients with intra-thoracic lesions than without (t-Student test; both <0.05). Furthermore, at multivariate analysis, a high malignancy risk and a FDG uptake > 2 point score in the lung nodule were predictors of intra-thoracic pathological uptake (both p<0.05).

Conclusion: FDG PET/CT by 4 point scale assessment has an acceptable performance in patients with SPN. Considering semi-quantitative continuous data (i.e SUVmax/SUVmeanBP ratio) the accuracy significantly improve, particularly in patients with intermediate and high risk of malignancy. Moreover, this ratio can be useful for the evaluation of disease spread in intra-thoracic site. Finally, stratification for risk category and FDG uptake in the lung nodules are predictors of intra-thoracic pathological sites.