Two Faces of NOTCH1 in Childhood Lymphoblastic T-Cell Neoplasia: Prognostic Divergence of Mutational and Structural Aberrations.

In pediatric patients, T-cell lymphoblastic lymphoma (T-LBL) survival exceeds 80%. Relapse remains associated with limited curative options. Frontline treatment is largely extrapolated from T-cell acute lymphoblastic leukemia (T-ALL) treatment, reflecting the ongoing debate, whether both entities represent distinct diseases or variants within one spectrum. This review focuses on T-LBL, summarizing shared and distinct clinical, pathological, and biological features in comparison to T-ALL. We address diagnostic and staging challenges, and current limitations of clinical risk stratification. Biomarkers, such as genetic variants in NOTCH1/FBXW7, are discussed in the context of dynamic risk assessment. Particularly emphasizing the molecular landscape of T-LBL and recurrent pathway alterations. NOTCH1 emerges as central determinant of disease biology. Activating NOTCH1 mutations (NOTCH1mut) are frequently associated with favorable outcomes and used for risk stratification in the ongoing trial LBL 2018 (EUCT number: 2023-508101-24-00). NOTCH1 fusions resulting in excessive NOTCH1 signaling are associated with increased relapse incidences, suggesting that the intracellular amount of NOTCH1 differentiates between tumor suppressive versus tumor supportive activity. These findings are placed in the context of recently described NOTCH1 variants in T-ALL, reported to similarly cause aberrant NOTCH1 activation. Future studies may consider incorporating detailed NOTCH1 status to understand disease dynamics and enhance therapeutic strategies.