Baseline [F]FDG PET/CT characterization of extramedullary disease and prognostic value in relapsed/refractory B-cell acute lymphoblastic leukemia treated with CAR-T cells.

[PURPOSE] This study aimed to characterize the non-central nervous system extramedullary disease (non-CNS EMD) in patients with relapsed/refractory B-cell acute lymphoblastic leukemia (r/r B-ALL) and to evaluate the prognostic value of metabolic parameters derived from [F]FDG PET/CT imaging.

[METHODS] Patients with r/r B-ALL who received chimeric antigen receptor (CAR)-T cell therapy and underwent [F]FDG PET/CT before CAR-T cell therapy were retrospectively enrolled. Lesions were semi-automatically segmented using LIFEx software, based on a threshold of 41% of the maximal uptake value. The anatomical locations of FDG-avid lesions were summarized to delineate the characteristics of non-CNS EMD. Furthermore, metabolic parameters from FDG PET/CT (SUVmax, MTV, and TLG) as well as selected clinical and laboratory features were collected. These variables were categorized into two groups for survival analysis. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan-Meier method.

[RESULTS] A total of 81 B-ALL patients were included in this study. The most frequently observed non-CNS EMD lesions involved the lymph node, spleen, and kidney. After a median follow-up time of 23.7 months, multivariate analysis identified hemoglobin (Hb) and SUVmax (with a cut-off value of 7.0) as independent prognostic factors for PFS and OS. Patients with abnormal Hb levels exhibited significantly shorter PFS and OS compared to those with normal Hb levels (median PFS: 13.5 months vs. not reached, P = 0.004; median OS: 48.0 months vs. not reached, P = 0.010). Similarly, patients with SUVmax above the threshold had significantly reduced PFS and OS compared to those below the threshold (median PFS: 9.1 months vs. not reached, P ≤ 0.001; median OS: 27.0 months vs. 50.8 months, P = 0.020).

[CONCLUSION] [F]FDG PET/CT effectively visualizes extramedullary infiltration in patients with B-ALL, and these non-CNS EMD lesions were also associated with clinical outcomes. SUVmax serves as a valuable predictive biomarker for both PFS and OS.