[Congenital leukemia showing lineage switch following induction chemotherapy and attaining long-term remission after HLA-haploidentical stem cell transplantation].

: Congenital leukemia is a rare subgroup of childhood leukemia. Lineage switches in leukemic cells are relatively rare events, which have been occasionally reported in congenital leukemia. To the best of our knowledge, the survival of congenital leukemia patients with lineage switch has not been previously documented. This lack of documentation may be attributable to extremely poor prognosis of these patients. We describe a case of a newborn female with initial diagnosis of MLL-AF4 positive B-precursor acute lymphoblastic leukemia, who developed lineage switch to acute monocytic leukemia following the induction therapy. Although morphological remission was temporary, she received an HLA-haploidentical bone marrow transplant from her father with non-remission status because of an early relapse at the age of 4 months. Despite many difficulties such as graft-versus-host disease, growth impairment, and psychomotor retardation, she remained in remission for 3 years and 7 months after the transplant. This successful outcome suggests that the graft-versus-leukemia effect was potentially accomplished in the patient. Taken together, early HLA-haploidentical stem cell transplant following remission is required for congenital leukemia patients with lineage switch, and it may be an effective alternative for refractory patients.