A long-term survivor of congenital KMT2A-R B-lymphoblastic leukemia with persistently positive bone marrow MRD and multiple CNS relapses.

Here we describe the case of an infant incidentally diagnosed with congenital KMT2A-rearranged (KMT2A-r) B-cell ALL on Day of Life 4. He received the first dose of intrathecal methotrexate on DOL 5, and induction systemic therapy on DOL 6. He demonstrated morphologic remission at the end of induction but had positive bone marrow. Minimal residual disease (MRD) was 1.4%. He experienced isolated CNS disease after consolidation and immunotherapy. At 8 months of age he underwent hematopoietic stem cell transplantation (HSCT). At 14 months of age he had medullary and CNS relapse, and at 16 months of age underwent CD19 CAR-T therapy. At 6 years of age he remains in remission with tolerable developmental delays and a good quality of life.