1261P - Comparison 18F-FDG-PET/CT criteria for prediction of therapy response and clinical outcome in patients with metastatic melanoma treated with ipilimumab and PD-1 inhibitors

Abstract

BackgroundImmune checkpoint inhibitors (ICIs) acting against CTLA-4 and PD-1 represent a strenght therapy in patients (pts) with metastatic melanoma (MM). Antineoplastic activity of ICIs through the activation of immune cells in tumor lesions raised challenge in evaluation of treatment response by imaging. Aim of this study was to compare diagnostic accuracy of different 18F-FDG PET/CT parameters (Metabolic Tumor Volume, MTV; Total Lesion Glycolisis, TLG; Maximum Standardised Uptake Value, SUVmax) to predict therapy response and clinical outcome in pts with MM treated with Ipilimumab (Ipi) and Nivolumab (Nivo) or Pembrolizumab (Pem) and to check for accuracy differences specific for the class of treatment. Methods57MM pts receiving Ipi (25) or PD-1 inhibitors (Nivo 19; Pem 13) who performed a 18F-FDG PET/CT scan at the beginning (PET0) and after completion of Ipi or during anti PD-1 (PET1), were retrospectively evaluated. Response at PET1 was classified as PD, SD, PR and CR according to RECIST 1.1, EORTC criteria and by percentage change of MTV and TLG (cut off values: +43% for PD and -43% for PR, calculated by ROC analysis) of up to 5 target lesions. PET Response Evaluation Criteria for Immunotherapy (PERCIMT) were assessed alone and with the previously described parameters. Performance of each criteria at PET1 to predict pts having clinical benefit (CR, PR and SD) and no clinical benefit (PD) at 6 months since starting ICIs were assessed and correlated to time-to-progression. ResultsFor Ipi pts group, best predictors of response were: variation of MTV (Sensitivity 1; Specificity 0.84; accuracy 0.96) and TLG (Se 0.89; Sp; 93.8; acc 0.92), with PERCIMT criteria for progressive disease. In anti-PD1 group overlapping predictivity values were found for EORTC, MTV and TLG (Se 0.95; Sp 1; Acc 0.97). Reliability of above parameters was also confirmed in predicting pts progression free survival at 12 and 24 months. Conclusions18F-FDG PET/CT performed 3 months later the first administration could predict response to ICIs and long-term patient clinical outcome. Performance of 18F-FDG PET/CT parameters and criteria in predicting response to ICIs is influenced by the class of treatment. Legal entity responsible for the studyLocal Ethic committee. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.