ETP-ALL

ETPs are recent immigrants from the bone marrow (BM) to the thymus, derived from hematopoietic stem cells, which retain a certain level of multilineage pluripotency.7,8 By gene expression profiling, ETP cells share similarities with hematopoietic stem cells and myeloid progenitor cells.5 The definition of ETP-ALL/LBL is based on the immunophenotype of the leukemic cells, which are typically CD1a−, CD8−, CD5− (dim), and positive for 1 or more stem cell or myeloid antigens.5 In the World Health Organization (WHO) classification, ETP-ALL/LBL falls within the early T-ALL/LBL category. ETP ALL has been reported in 11% to 12% of childhood T-ALL/LBL5,9 and in 7.4% of adult T-ALL/LBL.9 ETP-ALL/LBL is also characterized by a distinct molecular profile with a lower incidence of NOTCH1 mutations and frequent presence of FLT3 and DNMT3A mutations.6,10-12