T-cell lymphoblastic lymphoma in children, adolescents and young adults.

T-cell lymphoblastic lymphoma (T-LBL) is the second most common subtype of non-Hodgkin lymphoma (NHL) in children and adolescents. T-LBL shares considerable biological and clinical features with T-cell acute lymphoblastic leukaemia (T-ALL). The two entities are clinically distinguished by the extent of bone marrow (BM) involvement at diagnosis, with T-ALL defined by ≥25% blasts in the BM. Although the WHO classifies T-LBL and T-ALL as a single entity, emerging data suggest relevant clinical and molecular differences. This review focuses on T-LBL in paediatric patients, summarizing current knowledge on its clinical presentation, immunophenotype and molecular landscape. We further explore age-associated genomic patterns, recurrent mutations and chromosomal aberrations, with a particular focus on their prognostic relevance. Notably, recent studies have identified NOTCH1-fusions as exclusive to paediatric T-LBL, absent in T-ALL, and are associated with an increased risk of relapse. We highlight the limited applicability of measurable residual disease, lack of harmonized risk stratification and the need for T-LBL-specific treatment adaptations. Ultimately, this review emphasizes the urgent need for biologically informed, risk-adapted treatment strategies and collaborative research efforts to advance care and outcomes of paediatric patients with T-LBL.