Genomic variant profiling in blast-phase paediatric chronic myeloid leukaemia: Predisposing and driving alterations.

Paediatric blast-phase chronic myeloid leukaemia (CML-BP) is a rare and serious condition. Of 231 paediatric patients enrolled in the German CML-PAED-II registry between January 2007 and September 2023, 25 individuals (11%) were diagnosed with CML-BP. To identify genetic variants associated with early onset and disease transformation, we performed whole genome sequencing (WGS), deep targeted sequencing and cytogenetic analyses in 19 cases with de novo (n = 11) or secondary (n = 8) CML-BP and sufficient available biomaterial. Copy number variants (CNVs) were more frequent than single nucleotide variants (SNVs) and more prevalent in secondary than in de novo CML-BP. Recurrent pathogenic somatic SNVs were observed in ABL1 (n = 5, 24%), RUNX1 (n = 2, 12%) and ASXL1 (n = 2, 12%). Nine patients (47%) carried pathogenic germline (n = 8) or somatic (n = 1) variants in either of the genes ATM, CHEK2, FANCM, HERC2, NBN, RAD54B, RECQL4, SETD2 or TP63 belonging to the DNA damage response (DDR). Within a comparison cohort of 19 patients with chronic phase paediatric CML, only one individual (5%) exhibited a pathogenic DDR germline variant. Our study provides novel pathogenetic insights into paediatric CML-BP. The identification of pathogenic DDR-associated germline variants suggests a genetic predisposition with potential implications for patients and families concerning cancer treatment and surveillance.