This finding has been followed up by a report showing that 2 of 7 patients with mixed lineage leukemia (MLL)-rearranged B-ALL relapsing with CD19-negative AML following treatment with CD19 CAR-T cells (24) and a recent case report where a pediatric patient with TCF3-ZNF384 fusion-positive B-ALL had a myeloid switch after therapy (25). The gene discussed is TCF3; the disease is acute lymphoblastic leukemia.