Optical Genome Mapping for Detection of BCR::ABL1-Another Tool in Our Toolbox

Background:BCR::ABL1 fusion is mostly derived from a reciprocal translocation t(9;22)(q34.1;q11.2) and is rarely caused by insertion. Various methods have been used for the detection of t(9;22)/BCR::ABL1, such as G-banded chromosomal analysis, fluorescence in situ hybridization (FISH), quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) and optical genome mapping (OGM). Understanding the strengths and limitations of each method is essential for the selection of appropriate method(s) of disease diagnosis and/or during the follow-up. Methods: We compared the results of OGM, chromosomal analysis, FISH, and/or RT-PCR in 12 cases with BCR::ABL1. Results:BCR:ABL1 was detected by FISH and RT-PCR in all 12 cases. One case with ins(22;9)/BCR::ABL1 was cryptic by chromosomal analysis and nearly missed by OGM. Atypical FISH signal patterns were observed in five cases, suggesting additional chromosomal aberrations involving chromosomes 9 and/or 22. RT-PCR identified the transcript isoforms p210 and p190 in seven and five cases, respectively. Chromosomal analysis revealed additional chromosomal aberrations in seven cases. OGM identified extra cytogenomic abnormalities in 10 cases, including chromoanagenesis and IKZF1 deletion, which were only detected by OGM. Conclusions: FISH offers rapid and definitive detection of BCR::ABL1 fusion, while OGM provides a comprehensive cytogenomic analysis. In scenarios where OGM is feasible, chromosomal analysis and RT-PCR may not offer additional diagnostic value.