Early Lineage Switch from T-Acute Lymphoblastic Leukaemia to Common B-All

Leukaemic  stem  cells  have  heterogenous  differentiation  potential.  The immunophenotypes of blast cells are usually consistent throughout the disease course even at relapse.  Rarely, blast cells may undergo a ‘lineage switch’ during the course of disease especially during relapse. We would like to highlight such  a  case in  a 10- year  old  boy  who  presented  with  a  two  weeks  history  of  lethargy,  poor  appetite,  low grade  fever,  respiratory  distress,  cardiac  failure,  generalized  oedema  and hepatosplenomegaly.  Full  blood  count  showed  a  leucocyte  count  of  41.5x109/L  and platelet  count  of  37x109/L.  The  peripheral  blood  film  showed  presence  of  numerous blast cells. Bone marrow aspiration revealed a hypercellular marrow, which consisted of mainly blast cells with high nuclear to cytoplasmic ratio and inconspicuous nucleoli. Immunophenotyping and cytochemistry results were consistent with the diagnosis of T- cell  acute  lymphoblastic  leukaemia.  The  patient  achieved  remission  after  treatment with  UK  ALL  97  protocol,  regime  B  chemotherapy.  However,  he  relapsed  seven months after the initial diagnosis with 26% blast cells in the bone marrow aspirate. The majority was L1 blast cells admixed with some L2 blast cells. Immunophenotyping was consistent  with  common  precursor  B  acute  lymphoblastic  leukaemia.  The  treatment was changed to a more lineage specific chemotherapy. Nonetheless, the patient never achieved remission and was planned for palliative management. This case illustrated a unique and rare case of rapid lineage switch from T-cell acute lymphoblastic leukaemia to common precursor B-cell acute lymphoblastic leukaemia.