The Groundbreaking Validation of Whole Genome Sequencing (WGS) for a Comprehensive Genetic Profiling of Childhood B-cell ALL.

Objectives: A new study demonstrated the power of WGS to comprehensively and accurately profile the genetic abnormalities in cases of childhood B-ALL that were previously studied with standard cytogenetics, FISH and MLPA (Ryan et al., 2023). Two cohorts with a total of 210 patients were studied. One cohort carried cytogenetic abnormalities of known significance (n=38). The other cohort (n=172) lacked cytogenetic abnormalities detectable by standard methods (B-other ALL group), and was treated within the UKALL2003 clinical trial. The WGS approaches used were a tumor-normal (T-N) pipeline and a tumor-only (T-only) pipeline. Most patients (202/210) carried a distinct abnormality already known or a new one that defined a genetic subtype. WGS identified almost all the abnormalities in the cohort with typical cytogenetic abnormalities previously detected (37/38 in the T-only pipeline, 34/38 in the T-N pipeline). The B-other ALL cohort showed two types of abnormalities by WGS. Some were cytogenetic abnormalities emblematic of B-ALL that were missed by previous standard methods (19/172 cases) due to poor samples or incomplete testing at the time of diagnosis. The remaining abnormalities were cryptic (145/153 cases) and defined genetic subtypes. Some new molecular variants emerged with WGS, the profile of PAX5 rearrangements and the ETV6::RUNX1-like subtype was characterized in more detail, and the detection of DUX4 rearrangements was markedly improved by a novel bioinformatic pipeline. Whole transcriptome sequencing (WTS) conducted in a subset of 85 patients was consistent with the results of WGS and standard cytogenomic techniques. This study validated the diagnostic use of WGS to uncover and characterize in detail the genetic aberrations in pediatric B-ALL. As a result, Ryan et al. endorsed the routine use of WGS to discover more abnormalities of clinical significance that define new genetic subtypes, as well as to improve diagnosis, risk stratification, and therapy.