[Lineage switch from T-lymphoblastic leukemia to myeloid leukemia at relapse]

A 38-year-old woman was referred to our hospital because of fever, general malaise, and abnormal blood count. The white blood cell count was 19,500/µl, with 72% lymphoblast. Bone marrow examination showed increased cellularity with 94% lymphoblast. Flow cytometry revealed the following T-cell lineages: cyCD3 (+), CD5 (+), CD7 (+), and CD34 (+). Chromosome analysis revealed hypodiploidy. The patient was diagnosed with early T-cell precursor lymphoblastic leukemia (ETP-ALL). After two cycles of induction chemotherapy, she achieved complete remission, but the disease relapsed after one cycle of consolidation therapy. At the time of relapse, leukemic cells were myeloperoxidase positive and showed a loss of T-cell surface antigen, suggesting that a lineage switch occurred. The patient did not respond to the second induction therapy. She subsequently received 3+7 (idarubicin+cytarabine) for acute myeloid leukemia (AML), but she deceased due to refractory leukemia. At the time of relapse, genome sequencing was performed and mutations of NRAS, TP53, and MLLT-PICALM fusion genes were revealed. Here, we report a case of ETP-ALL who relapsed with a lineage switch to AML in concordance with refractory disease.