Prognostic value of early post-treatment 18F-FDG PET/CT in diffuse large B-cell lymphoma patients receiving chimeric antigen receptor T-cell therapy.

Purpose: To evaluate the prognostic value of early post-treatment ¹⁸F-FDG PET/CT in diffuse large B-cell lymphoma (DLBCL) patients undergoing chimeric antigen receptor T-cell (CAR-T) therapy.

Methods: In this retrospective study, 159 patients referred for imaging prior to CAR-T therapy between January 2018 and May 2023 were reviewed. Of those, 51 with both baseline pre-infusion and one-month post-treatment ¹⁸F-FDG PET/CTs were included. ¹⁸F-FDG PET/CT parameters were derived, including standard uptake values (SUVs), metabolic tumour volume (MTV), total lesion glycolysis (TLG), and Dmax. Additionally, the delta changes from the baseline were calculated. Time to progression/death was documented. For progression-free survival (PFS) and overall survival (OS), univariate analysis was performed using the Kaplan-Meier method. The significance of the difference was measured using the Mantel-Cox log-rank test. Significant parameters entered the multiple Cox regression.

Results: Overall, 51 patients (mean age = 56y) entered the study. All had Deauville scores of 4 (14/51; 28%) or 5 (37/51; 72%) at baseline. At one month, 28% of patients showed a complete metabolic response, while 72% had ¹⁸F-FDG-avid significant residual disease. Investigating those with residual disease, SUVmax, SUVpeak, SUVmax-to-Liver ratio and MTV were significantly lower in the one-month post-treatment scan. For PFS evaluation, serum LDH, one-month post-treatment SUVmax-to-liver ratio, one-month post-treatment TLG, and baseline Dmax entered the multivariate analysis. The one-month post-treatment SUVmax-to-liver ratio (Hazard ratio [HR] = 5.21; p = 0.004) and baseline Dmax (HR = 13.8; p = 0.013) retained significance, being independent predictors of PFS. For OS, serum LDH, delta SUVmean-to-liver ratio, delta percentage TLG, and one-month post-treatment Dmax were included in the multivariate analysis. The delta percentage TLG (HR = 4.37; p = 0.023) remained significant as an independent predictor of OS.

Conclusion: Early post-treatment ¹⁸F-FDG PET/CT can provide valuable prognostic information for DLBCL patients receiving CAR-T. The most significant predictors of outcomes would be the baseline extent of the disease, one-month post-treatment avidity, and changes in the metabolic burden from baseline.