Pseudoprogression of extramedullary disease in relapsed acute lymphoblastic leukemia after CAR T-cell therapy.

Background: CD19-targeted chimeric antigen receptor (CAR) T-cell therapy has emerged as a powerful immunotherapy in relapsed or refractory B-cell acute lymphoblastic leukemia. The changes in extramedullary (EM) disease in pediatric relapsed or refractory B-cell acute lymphoblastic leukemia after CAR T-cell therapy have rarely been reported. Materials & methods: A child with relapsed B-ALL was treated with CAR T-cell therapy. Bone marrow morphological examination, minimal residual disease, fusion mutation and radiological evaluation of the EM disease were performed before and after CAR T-cell infusion. Results: Radiological assessment revealed a distinct asymptomatic pseudo progression of EM involvements on day 16 after CAR T-cell infusion. Conclusion: Pseudoprogression of EM disease indicates heterogeneous immune-related patterns of response in patients treated with CAR-T therapy. Such patients should be closely monitored and practical immune-related response criteria should be developed for them.