marker chromosomes are a significant mechanism of high-level RUNX1 gene amplification in hematologic malignancies

To understand the cytogenetic mechanisms responsible for multiple RUNX1gene copy numbers in hematologic malignancies, we analyzed the chromosomaland molecular cytogenetic findings in bone marrow or peripheral blood samplesof individuals who were diagnosed with acute myeloid leukemia (AML),myelodysplastic syndrome (MDS), or acute lymphoblastic leukemia (ALL).Included in the analysis were 113 consecutive samples received in ourlaboratory between January 2005 and June 2007. Bone marrow and/orperipheral blood samples were characterized using conventional G-bandingtechniques and fluorescent in situ hybridization (FISH) techniques withcommercially available RUNX1/RUNX1T1 or ETV6/RUNX1 dual-color fusionprobes. Eighty-one (72%) of the 113 samples showed an abnormal karyotypeand/or abnormal FISH results. Eight of these had, by interphase FISH,RUNX1/RUNX1T1 or RUNX1/ETV6 fusion, and 19 had three or moreRUNX1 signals not related to fusion with RUNX1T1 or ETV6 gene. Of the 19cases with multiple RUNX1 gene signals, 5 had high-level RUNX1amplification — defined as 5 or more RUNX1 signals in interphase cells —whereas the remaining 14 had 3–4 RUNX1 signals. Four of the five tumors withhigh-level RUNX1 amplification were myeloid disorders — three cases ofAML and one case of MDS. The karyotypes of tumors with high-levelamplification of RUNX1 were significantly characterized by the presence ofmarker chromosomes that harbored extra copies of the RUNX1 gene comparedwith tumors that had three to four RUNX1 gene signals (P = 0.026, Fisher sexact test). Our findings show that high-level RUNX1 amplification, especiallyin myeloid disorders, often results from marker chromosomes harboring extracopies of the RUNX1 gene . This suggests that amplification of RUNX1 inthese tumors may be secondary to a previous rearrangement of 21q22, whichlater evolved into a complex marker chromosome as part of tumor progressio