Can 3'-deoxy-3'- 18 F-fluorothymidine or 2'-deoxy-2'- 18 F-fluoro-d-glucose PET/CT better assess response after 3-weeks treatment by epidermal growth factor receptor kinase inhibitor, in non-small lung cancer patients? Preliminary results

The objectives of this study was to study the diagnostic efficacy of 3'-deoxy-3'-fl uorine-18-fl uorothymi dine ( 18 F-FLT) and of 2’-deoxy-2’18 F-fl uoro-d-glucose ( 18 F-FDG) positron emission tomography/computed tomography (PET/CT) for response evaluation following three weeks treatment by epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) in non small cell lung cancer (NSCLC) patients. Fifteen patients of advanced stage (IIIB-IV) NSCLC planned for oral 1st or 2nd/3rd line EGFR-TKI treatment were enrolled in the study. Baseline, prior to treatment, and follow-up after three weeks, 18 F-FLT and 18 F-FDG PET/CT imaging was performed in all patients. The standard uptake lean body mass (SUL peak ) and total lesion glycolysis (TLG) values of the hottest lesions were calculated in all patients using semi-quantitative analysis. Statistical analysis on PET semi-quantitative data was used to evaluate the overall survival (OS) and progression free survival (PFS). The patients were either classifi ed as responders or non-responders or at a steady state according to the PET response criteria in solid tumors (PERCIST). The receiver operating characteristic curve (ROC) analysis was done on the 18 F-FDG PET/CT clinical responders, to derive the cutoff values on the corresponding data sets between responders and non responders. Results showed that in responders 18 F-FDG SUL peak values better predicted OS and PFS values when compared to 18 F-FLT SUL peak values and also were a better predictor of OS as compared to the TLG values. In responders, the ROC analysis carried out on 18 F-FLT PET/CT imaging data in responders indicated a decrease of ≥22% in SUL peak and a decrease of ≥0.7 in absolute values. Three (3/15) patients developed resistance to EGFR-TKI treat ment at 3 months of follow-up. In conclusion , in both responders and in non responders, patients with NSCLC treated for 3 weeks by EGFR-TKI, both OS and PFS were better predicted by 18 F -FDG SUL peak than by 18 F-FLT SUL peak . Although, the difference was only borderline, yet, 18 F -FDG SUL peak was a better predictor of OS compared to TLG values. However, to validate these fi ndings, studies need to be carried in a larger number of patients.