Acute Lymphoblastic Leukemia Switch Lineage upon Relapse to Acute Bilineage Leukemia: A Case Report

Although acute leukemia commonly relapses in adults, the conversion of leukemic cell lineage (lymphoid or myeloid) upon relapse has rarely taken place. “Lineage switch” is a term widely used to define the leukemic lineage transformation as assessed by morphology, cytochemistry, and immunophenotyping from diagnosis to relapse. In most lineage switch cases, B-cell lymphoblastic leukemia/lymphoma relapses as acute myeloid leukemia or vice versa. Here, we report an exceedingly rare case of T-cell acute lymphoblastic leukemia relapsing as mixed-phenotype acute leukemia.