Frequent TCR rearrangements in pediatric B-cell lymphoblastic acute leukemia: genomic and phenotypic features.

T-cell receptor (TCR) loci undergo complex V(D)J rearrangements during T-cell maturation. However, errors in this process can cause TCR promoters and enhancers to aberrantly fuse with oncogenes, leading to their overexpression and the development of T-cell acute lymphoblastic leukemia (T-ALL). Unexpectedly, in a retrospective study of 97 pediatric B-ALL cases, all diagnosed according to WHO criteria at a single institution, we identified a subgroup of B-ALL harboring TCR fusion. These fusions involved diverse partner genes, including LINC01656, TBC1D10B, TCL1A/TCL1B, CDKN2A, CEBPB/G, and AHI1. Patients with TCR fusions showed a gene expression profile enriched in hematopoietic stem cell (HSC) signatures and frequently carried other adverse genomic markers, such as CDKN2A/B alterations and RAS pathway activation. Clinically, TCR-rearranged B-ALL patients were associated with increased risk (P = 0.005) and had higher minimal residual disease (MRD) at day 19 (P = 0.034), and may benefit from MRD-based risk-directed therapy. Our study highlights frequent TCR fusions in B-ALL, suggesting a stem cell-derived leukemia with potential differentiation into both B-cell and T-cell lineages.