BackgroundChimeric antigen receptor T-cell therapy (CART) prolongs survival for patients with refractory or relapsed lymphoma. Discrepancies among different response criteria for lymphoma under CART were recently shown. Our objective was to evaluate reasons for discordance among different response criteria and their relation to overall survival.MethodsConsecutive patients with baseline and follow-up imaging at 30 (FU1) and 90 days (FU2) after CART were included. Overall response was determined based on Lugano, Cheson, response evaluation criteria in lymphoma (RECIL) and lymphoma response to immunomodulatory therapy criteria (LYRIC). Overall response rate (ORR) and rates of progressive disease (PD) were determined. For each criterion reasons for PD were analyzed in detail.Results41 patients were included. ORR was 68%, 68%, 63%, and 68% at FU2 by Lugano, Cheson, RECIL, and LYRIC, respectively. PD rates differed among criteria with 32% by Lugano, 27% by Cheson, 17% by RECIL, and 17% by LYRIC. Dominant reasons for PD according to Lugano were target lesion (TL) progression (84.6%), new appearing lesions (NL; 53.8%), non-TL progression (27.3%), and progressive metabolic disease (PMD; 15.4%). Deviations among the criteria for defining PD were largely explained by PMD of preexisting lesions that are defined as PD only by Lugano and non-TL progression, which is not defined as PD by RECIL and in some cases classified as indeterminate response by LYRIC.ConclusionsFollowing CART, lymphoma response criteria show differences in imaging endpoints, especially in defining PD. The response criteria must be considered when interpreting imaging endpoints and outcomes from clinical trials.Supplementary InformationThe online version contains supplementary material available at 10.1186/s40644-023-00566-7.