Myeloid lineage switch following chimeric antigen receptor T-cell therapy in a patient with TCF3-ZNF384 fusion-positive B-lymphoblastic leukemia.

A pediatric patient diagnosed initially with B-lymphoblastic leukemia (B-ALL) relapsed with lineage switch to acute myeloid leukemia (AML) after chimeric antigen receptor T-cell (CAR-T) therapy and hematopoietic stem cell transplant. A TCF3-ZNF384 fusion was identified at diagnosis, persisted through B-ALL relapse, and was also present in the AML relapse cell population. ZNF384-rearrangements define a molecular subtype of B-ALL characterized by a pro-B-cell immunophenotype; furthermore, ZNF384-rearrangements are prevalent in mixed-phenotype acute leukemias. Lineage switch following CAR-T therapy has been described in patients with KMT2A (mixed lineage leukemia) rearrangements, but not previously in any patient with ZNF384 fusion.