Purpose or Case Report: Most pediatric patients with acute lymphoblastic leukemia (ALL) demonstrate tumor remission during the first weeks or months after Chimeric Antigen Receptor (CAR) T-cell therapy. However, 30–60% of patients ultimately relapse, highlighting the need for early, non-invasive risk stratification after treatment. 18FDG PET/MR can assess the bone marrow without biopsy, but its prognostic utility after CAR T-cell therapy remains unexplored. The purpose of the study was to determine if changes in bone marrow metabolic activity on 18F-FDG PET/MR at day 28 after CAR T-cell therapy is associated with five-year survival in children with ALL.
Methods & Materials: We conducted a single-center retrospective study of 14 patients with ALL (median age: 16 years, interquartile range (IQR) 6 years; 8 females, 6 males) who underwent 18F-FDG PET/MRI before and after CAR T-cell therapy. Patients were classified based on five-year survival outcomes as survivors (n = 10) and non-survivors (n = 4). The mean standardized uptake value (SUVmean) of the bone marrow was measured at baseline and at day 28 after CAR T-cell therapy. Median bone marrow SUVmean values as well as percent blasts and myelocytes in bone marrow biopsies were compared between survivors and non-survivors using the Wilcoxon signed rank test.
Results: At baseline, the median bone marrow SUVmean was not significantly different between survivors (median 2.65, IQR 1.36) and non-survivors (median 2.60, IQR 0.49. At 28 days after CAR T-cell therapy, the bone marrow SUVmean of survivors (median 1.61, IQR 0.47) was significantly smaller compared to non-survivors (median 4.83, IQR 1.83; p=0.004). In addition, survivors demonstrated significantly lower quantities of blasts (median 1 % IQR 0.72) and myelocytes (7.06 % IQR 5.19) in bone marrow biopsies at day 28 compared to non-survivors (15 % IQR 27; p = 0.016 and (12.5 %, IQR 8.09, p = 0.043, respectively).
Conclusions: Early changes in bone marrow metabolic activity on 18F-FDG PET/MR at day 28 after CAR T-cell therapy are associated with five-year survival in children with ALL.