P464: Compared to Classical Cytogenetics Optical Genome Mapping (Ogm) Detects Multiple Additional Structural Chromosomal Aberrations in Pediatric Acute Myeloid Leukemia (Aml)

Abstract

Background:Background: AML is the 2nd most frequently diagnosed blood cancer in children affecting approximately 130 patients annually in Germany. Pediatric AML is a heterogeneous malignancy that has multiple genetic aberrations. This is relevant for classification, prognosis and selection of optimal therapy. To detect these alterations established procedures (karyotyping, FISH, RNA-based techniques) are used with well-known limitations (resolution of karyotyping and FISH, respectively; cell cultivation is necessary to generate metaphases; cost-intensiveness; necessity of experienced and intensively trained staff). OGM is an emerging technique addressing these limitations. Based on extraction of ultra-high weight DNA followed by fluorescent labelling at the sequence CTTAAG a barcode-like pattern of the genomic DNA is created. The DNA strands labelled in this way are stretched and drawn as single ultra-long fragments through nanochannels. The results are translated into molecule maps which are compared to the reference genome (resolution down to 500 bp) allowing the identification of genetic alterations. This method combines high resolution with picturing almost whole chromosomes without cell cultivation. Aims: Aims:The aim of this study was to test to what extend OGM might supplement classical cytogenetics (CCG) to detect risk defining genetic aberrations at initial diagnosis in pediatric patients with AML. Methods:Methods: We analyzed 24 specimen of pediatric AML, MPAL and bilineage leukemia patients by OGM starting from stored frozen material (bone marrow, peripheral blood) obtained at initial diagnosis. Results of OGM were compared with karyotyping and FISH. Primer walking and breakpoint spanning PCR were used to validate newly detected aberrations by OGM in selected cases. Applying breakpoint-spanning PCR, validated aberrations were used as markers for assessment of minimal residual disease (MRD) in selected cases during AML treatment. Results:Results: Overall, we detected discrepant results between CCG and OGM in 17/24 (70%) cases including 9 cases in