An old leukaemia in young patients-Genetic characteristics of paediatric chronic myeloid leukaemia.

Chronic myeloid leukaemia (CML) accounts for 2% of leukaemias in children and 9% in adolescents. While the BCR::ABL1 fusion gene remains a hallmark across all age groups, emerging evidence suggests that paediatric CML exhibits unique biological and clinical characteristics compared to its adult counterpart. Children often present with more aggressive clinical features and show distinct treatment response patterns. Recent genomic and transcriptomic studies have highlighted a higher prevalence of germline variants in haematopoiesis-related genes and unique cytogenetic alterations, as well as age-specific distributions of BCR and ABL1 breakpoints. Transcriptomic profiling of paediatric CML stem cells reveals differential expression signatures that suggest the presence of distinct signalling networks. Somatic mutations-particularly in ASXL1-are observed at diagnosis in some children, though their prognostic relevance remains uncertain. Additionally, while the BCR::ABL1 transcript subtype is known to affect treatment-free remission in adults, its role in paediatric CML is still unclear. Collectively, these findings support the notion that paediatric CML may constitute a biologically distinct disease rather than simply a younger form of adult CML. To advance risk stratification and develop age-specific treatment approaches, larger international studies and comprehensive genomic analyses are urgently needed.