Dual-time-point [18F]FDG-PET/CT as a prognostic biomarker in patients with pleural mesothelioma undergoing immunotherapy

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[ 18 F]FDG PET/CT provides a non-invasive assessment of tumour glucose metabolism. While conventional PET/CT captures a single time point, dual-time-point PET/CT (DTP-PET) evaluates metabolic dynamics by acquiring images at two defined times after injection. This study investigated whether the change in [ 18 F]FDG uptake between 60 and 120 min—retention index (RI)—predicts clinical outcomes in patients with pleural mesothelioma (PM) receiving immunotherapy. Patients from the NIPU trial (NCT04300244) underwent DTP-PET at baseline ( n = 50) and/or week-5 ( n = 45), with 42 completing both. Peak SUV was measured in a 2-cm spherical volume of interest centred on the most avid lesion at 60 and 120 min, and RI was calculated as the percentage change between the two. Survival (OS, PFS) was analysed using Kaplan–Meier curves and Cox proportional hazards models based on tertiles of RI and SUV 60min . Objective response and disease control were defined by mRECIST and iRECIST. Group comparisons used the Wilcoxon rank-sum test. At week-5, RI tertiles showed stepwise separation for both OS ( p = 0.038) and PFS ( p = 0.031), with the lowest tertile associated with the most favourable outcomes. SUV 60min tertiles were also significantly associated with OS ( p = 0.042) and PFS ( p = 0.043), though OS exhibited a non-monotonic pattern in which the middle tertile had the poorest survival. Objective responders displayed significantly lower RI and SUV 60min at week-5. Baseline RI tertiles were not associated with OS or PFS. Week-5 [ 18 F]FDG DTP-PET suggests prognostic value in PM patients receiving immunotherapy. Both RI and SUV 60min were associated with objective response. RI showed a consistent stepwise association with survival, whereas SUV 60min showed a non-monotonic relationship for OS. These findings are exploratory and require validation in larger cohorts. Further studies are warranted to explore underlying biological mechanisms. ClinicalTrials.gov NCT04300244. Registered 2020-03-09. https://clinicaltrials.gov/study/NCT04300244

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