Potential use of FDG-PET scan after induction chemotherapy in surgically staged IIIa-N-2 non-small-cell lung cancer: A prospective pilot study

Background: Clearance of viable tumour cells in mediastinal lymph nodes (ML N) by induction chemotherapy (IC) - so-called MLN downstaging - is an impor tant aspect of combined-modality treatment of N-2-NSCLC. Reassessment of ML N after IC by CT is far from accurate, while re-mediastinoscopy is often te chnically difficult. Based on our previous results with FDG-PET in the init ial staging of N-2 disease, we investigated whether PET after IC could be h elpful in predicting MLN downstaging and therapeutic outcome. Patients and methods. Patients underwent a first PET before IC. After three cycles of platinum-based IC, a second PET was performed before locoregiona l therapy, either surgery or radiotherapy. PET results were correlated with pathology of the MLN when available, and with survival. Results: Fifteen surgically staged N-2-NSCLC patients were prospectively in cluded. Locoregional therapy after IC consisted of surgery in nine and radi otherapy in six. Correlation with pathology of the nine resection specimens revealed that the accuracy of PET in predicting MLN downstaging was 100% ( six true negatives; three true positives), whereas for CT it was only 67% ( two false pos; one false neg). Reassessment with PET after IC was correlate d with the outcome after the entire combined modality treatment. Survival w as significantly better in patients with mediastinal clearance (P = 0.01) o r with a greater than 50% decrease in the Standardised Uptake Value (SUV) o f the primary tumour (P = 0.03) after IC. Conclusions: Mediastinal PET after IC accurately assesses pathologic MLN do wnstaging in N-2-NSCLC. The data suggest a possible correlation of early su rvival with mediastinal clearance and an important decrease of SUV in the p rimary tumour. Confirmation of these preliminary findings would establish P ET as a useful non-invasive tool to select patients for intensive locoregio nal treatment after IC.