A twist of fate – lineage switch in acute leukaemia

Acute leukaemia is classified as myeloid, lymphoid, or of ambiguous lineage.1 Conversions of leukaemic cell lineage are rare, occurring in <1% of childhood acute leukaemias.2 Historically, the vast majority of lineage conversions are described in childhood acute leukaemias following chemotherapy at relapse.3 Here, two cases of Philadelphia negative acute B-lymphoblastic leukaemia (B-ALL), with early lineage switch following pre-phase corticosteroid treatment, are presented. Both cases were negative for KMT2A rearrangements, a molecular aberration with an association for lineage conversions.3 The first case is an 18-month-old boy, initially diagnosed with B-ALL that converted to an acute myeloid leukaemia (AML). He was treated with induction treatment for AML, however reverted to a B-ALL phenotype following one course of treatment. He was thereafter successfully treated with an ALL-based protocol. The second case, a 60-year-old woman, was also initially diagnosed with B-ALL and rapidly switched to an AML following corticosteroid treatment. She unfortunately succumbed to her disease. In both cases, the genetic signature of the leukaemia remained constant despite the phenotypic evolution. Morphology, immunophenotyping, cytogenetics and molecular studies play a crucial role in the diagnosis of these rare lineage conversions, and accurate interpretation is essential to guide treatment and prognostication. References 1.Swerdlow SH, Campo E, Harris NL, et al. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. Lyon, France: IARC, 2008.2.Rossi JG, Bernasconi AR, Alonso CN, et al. Lineage switch in childhood acute leukemia: an unusual event with poor outcome. Am J Hematol 2012; 87: 890–7.3.Dorantes-Acosta E, Pelayo R. Lineage switching in acute leukemias: a consequence of stem cell plasticity? Bone Marrow Res 2012; 2012: 406796.