The role of 18 F-FDG PET in the differentiation between lung metastases and synchronous second primary lung tumours

Purpose In lung cancer patients with multiple lesions, the differentiation between metastases and second primary tumours has significant therapeutic and prognostic implications. The aim of this retrospective study was to investigate the potential of 18 F-FDG PET to discriminate metastatic disease from second primary lung tumours. Methods Of 1,396 patients evaluated by the thoracic oncology group between January 2004 and April 2009 at the Radboud University Nijmegen Medical Centre, patients with a synchronous second primary lung cancer were selected. Patients with metastatic disease involving the lungs served as the control group. Maximum standardized uptake values (SUVs) measured with 18 F-FDG PET were determined for two tumours in each patient. The relative difference between the SUVs of these tumours (∆SUV) was determined and compared between the second primary group and metastatic disease group. Receiver-operating characteristic (ROC) curve analysis was performed to determine the sensitivity and specificity of the ∆SUV for an optimal cut-off value. Results A total of 37 patients (21 metastatic disease, 16 second primary cancer) were included for analysis. The ∆SUV was significantly higher in patients with second primary cancer than in those with metastatic disease (58 vs 28%, respectively, p < 0.001). The area under the ROC curve was 0.81 and the odds ratio for the optimal cut-off was 18.4. Conclusion SUVs from 18 F-FDG PET images can be helpful in differentiating metastatic disease from second primary tumours in patients with synchronous pulmonary lesions. Further studies are warranted to confirm the consistency of these results.