Karyotype with the presence of a cryptic rearrangement involving the BCR-ABL1 fusion gene may be found in chronic myeloid leukemia (CML) patients with apparently normal karyotype, or in cases where the t(9;22)(q34;q11) is not visible in a conventional cytogenetic analysis due to a secondary genetic event affecting another partner chromosome. This study confirmed that patients with apparently ‘normal’ karyotype may have the BCR-ABL1 rearrangement and that standard cytogenetic together with FISH analysis can be used to detect atypical hybridization patterns of the BCR-ABL1 fusion gene in patients with CML. Thus, the authors conclude that included data provide a precise molecular cytogenetic characterization of rare Philadelphia-negative/BCR-ABL1-positive rearrangements in patients with chronic myeloid leukemia treated with tyrosine kinase inhibitors.

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