Purpose or Case Report: Chimeric antigen receptor (CAR) T-cell therapy achieves remission in 80–90% of children with relapsed or refractory acute lymphoblastic leukemia (ALL), but only 20% in pediatric patients with solid tumors. Identifying early biomarkers of response could allow timely interventions for non-responders and support the optimization of effective combination therapies. The spleen plays a central role in immune regulation and lymphocyte trafficking, potentially affecting CAR T-cell expansion, persistence, and toxicity risk. The purpose of our study was to explore if pre treatment spleen to liver SUV ratio (SLR) measured on 18FDG PET/MR may correlate with their treatment outcomes.
Methods & Materials: We conducted a single-center retrospective study of 24 pediatric patients (14 with ALL and 10 with solid tumors, (median age: 16 years, interquartile range (IQR) 6 years; 10 females, 14 males) who underwent 18FDG PET/MR at baseline and clinical response assessment at day 28 after CAR T-cell infusion. Patients were stratified into two groups based on five-year survival outcomes (Group 1: survivors (n=17), Group 2: non-survivors (n=7). Spleen SUVmax, liver SUVmax and spleen to liver ratio (SLR) at baseline, as well as serum LDH levels at day 28 after therapy were compared between group 1 and 2, using Wilcoxon ram sum test. In addition, SLR and LDH data were correlated with Pearson’s linear regression analysis.
Results: Patients in Group 2 demonstrated significantly higher SLR values at baseline (median =1.1, IQR = 0.03) compared to Group 1 (median =0.905, IQR = 0.39, p= 0.006). In addition, group 2 demonstrated significantly higher LDH at day 28 (median =450 U/L, IQR = 123) compared to group 1 (230 U/L, IQR = 147; p = 0.044). SLR at baseline demonstrated moderate correlation with LDH levels at day 28 follow up (r = 0.406, p = 0.085, 95% CI = (-0.06, 0.73)).
Conclusions: Baseline spleen to liver ratio on 18FDG PET/MR was associated with poorer survival in pediatric patients undergoing CAR T-cell therapy. High baseline SLR may identify patients with pre-existing systemic immune activation and metabolic stress, leading to heightened inflammation (elevated LDH) and poor survival after CAR T-cell therapy.