Acute Myeloid Leukemia FISH Probes

Deletions in the long arm of chromosome 5 are the most common cytogenetic abnormalities in MDS and secondary AML. They're more prevalent in older patients, and occur frequently at diagnosis in alkylating-agent-related AML.

DEK/NUP214 fusion occurs in about 1% of AML and myelodysplastic syndromes. The abnormality increases cell proliferation via upregulation of mammalian target of rapamycin complex 1 (mTORC1) activity.

After trisomy 8, del(7q) is the second most common numerical abnormality in both adult and pediatric AML. It is associated with prior exposure to carcinogens or leukemogenic agents. The alteration is also more frequent in patients with complex karyotypes, like del(5q) and trisomy 8.

FGFR1-rearranged hematopoietic neoplasms are often initially diagnosed as myeloproliferative neoplasms (MPN), but rapid transformation to AML is common. So far, more than 15 FGFR1 fusion partner genes have been reported in blood and lymph malignancies.

Although the KIT receptor is expressed on the majority of AML blasts, KIT gene mutations are found exclusively in core binding factor (CBF)-AML, a subtype made up of patients with either t(8;21) or inv(16). Both mutations affecting D816 within the KIT tyrosine kinase domain 2 and insertion/deletions in exon 8 are also observed in CBF-AML.

MECOM-rearranged AML, with either inv(3)(q21q26.2) or t(3;3)(q21;q26.2), is a recently classified AML entity. MECOM houses both a hematopoietic stem cell factor that blocks myeloid cell differentiation and apoptosis, and a chromatin remodeler that is thought to contribute to chemotherapy resistance.

MLL rearrangements define a biologically and clinically distinct class of AML, characterized by few accompanying mutations and rapid disease course. These translocations fuse the amino-terminal portion of MLL to a partner gene (over 70 have been documented so far), creating a gain-of-function oncogene.

MYB encodes a transcription factor that's been shown to drive leukemia progression; AML cells can become addicted to high levels of MYB. The MYB protein is broadly expressed in immature hematopoietic cells, where it monitors the transcription of genes involved in lineage determination, cell proliferation, and differentiation.

CBFB/MYH11 fusion, generated by either inv(16)(p13.1q22) or the balanced translocation t(16;16)(p13.1;q22), is one of the most common de novo AML subtypes. The inversion is far more common (95%) than the translocation (5%). Both abnormalities have been documented across all age groups.

NCOA2 encodes a transcriptional coactivator for nuclear hormone receptors, including steroid, thyroid, retinoid, and vitamin D receptors. In AML, NCOA2 has been shown to participate in fusions with several different genes, including KAT6A and ETV6.

NUP98 rearrangements are recurrent across many leukemias, including de novo or therapy-related, with a myeloid or T-cell lymphoblastic phenotype. Translocations usually produce fusion genes with NUP98's N-terminal GLGF domain fused to the C-terminus of the partner gene.

PML/RARA fusion is a genetic hallmark of acute promyelocytic leukemia (APL), occurring in roughly 98% of cases. It also occurs as the sole genetic abnormality in 70-90% of patients; only a small minority harbor additional complex rearrangements.

Deletions in the long arm of chromosome 20 are common across myeloid malignancies, especially myeloproliferative disorders (MPD), myelodysplastic syndromes (MDS), and AML. The del20q minimum deleted region contains nine genes, including MYBL2 and PTPRT, the loss of which results in deregulation of hematopoietic progenitors.

RUNX1/RUNX1T1 fusion is found in 4-8% of AML cases. Patients with t(8;21)(q22;q22.1) are typically younger, of the M2 subtype, and harbor additional cytogenetic abnormalities - most often loss of sex chromosome, del(9q), and trisomy 8.

Amplified telomerase levels have been shown to extend survival for AML stem cells. Levels can be elevated by amplification of the TERT gene, which monitors telomere length and destruction. Low TERT activity is just as dangerous; TERT haploinsufficiency can give rise to bone marrow failure, a precursor to AML.