The Confirmatory Diagnostic Value of Whole Genome Sequencing (WGS) as a Standalone Test for Childhood B-cell ALL: The Results of a NOPHO Trials Cohort.

Objectives: The latest study with whole genome sequencing (WGS) in pediatric B-ALL validated its use as a standalone test to detect underlying clinically significant genetic abnormalities (Rezayee et al., 2023). This was a retrospective molecular survey in bone marrows previously collected and stored from 88 patients who were enrolled in NOPHO trials. The testing was done through 150 bp paired-end WGS applied to a paired analysis of leukemia-germline samples (L-N) (n=64), and to the analysis of leukemia-only samples (L) (n=88). The results demonstrated a full concordance between both WGS approaches and between the results from WGS and previous standard of care tests (SOCTs). All the mandatory aberrations that require testing in the current ALLTogether trial protocol were identified in 38 patients. In addition, WGS accurately identified the majority of aberrations characteristic of B-other ALL (35/36 cases), copy number abnormalities (CNAs) in eight critical genes or regions, CNAs that characterize the IKZF1plus profile, and the abnormalities in patients with Down syndrome. An adapted methodology was necessary for the detection of DUX4::IGH rearrangements in four patients. A comparison between sequencing coverages of 90X and 30X demonstrated that a lower 30X coverage was sufficient to detect all the relevant abnormalities. This successful testing was accomplished through filtering of WGS data focusing on just genes and genomic regions that are routinely implicated in pediatric B-ALL. As a result, it simplified the extraction of data and facilitated the interpretation of results. Overall, the precise identification of abnormalities that was accomplished by WGS allowed the assignment of patients to distinct genetic subtypes. The conclusion of this study was that WGS is quite reliable and can replace the use of SOCTs to profile pediatric B-ALL.