T‐cell lymphoblastic lymphoma in children, adolescents and young adults

Summary 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.