We describe a case of a four-year-old boy diagnosed with an Early T-cell Precursor Lymphoblastic Leukaemia. This type of leukaemia is recognised as a high-risk subgroup characterised by very early arrest in T-cell differentiation. Early T-cell Precursor Lymphoblastic Leukaemia cases have characteristic gene expression profiles, increased genomic instability and a distinct immature immunophenotype (CD1a–, CD8–, CD5+dim and positivity for at least one marker of stem cell or myeloid lineage). This type of leukaemia is associated with poor prognosis and a poor response to intensive chemotherapy, though this finding is still debated. Our patient displayed an inferior response to induction therapy. The main purpose of this report is to make Belgian physicians aware of this entity and its controversial prognostic significance.

(BELG J HEMATOL 2017;8(2):75–9)