However, whereas the genomic breakpoints in MLL tend to cluster in the 5' portion of the 8.3 kb breakpoint cluster region (BCR) in de novo and adult patients and in the 3' portion in infant leukemia patients and t-AML patients, those in both the AML1 and ETO genes occur in the same clustered regions in both de novo and t-AML patients.
This translocation is observed in patients with therapy-related myelodysplastic syndrome (MDS), with chronic myelogenous leukemia during the blast crisis (CML-BC), and with de novo or therapy-related acute myeloid leukemia (AML).
We recently demonstrated that 75% of de novo patient breakpoints in MLL mapped in the centromeric half of the BCR between two scaffold-associated regions (SAR), whereas 75% of the t-AML patient breakpoints mapped to the telomeric half of the BCR within a strong SAR.
Therefore, 74% of leukemia de novo and 25% of t-AML breakpoints map to the centromeric half of the breakpoint cluster region map between the two SARs; in contrast, 26% of the leukemia de novo and 75% of the t-AML patient breakpoints map to the telomeric half of the breakpoint cluster region that contains both the telomeric SAR and the topo II sites.