The t(3;5)(q25;q35) NPM1/MLF1 fusion has an incidence of approximately 0.5% in acute myeloid leukemia (AML) and has an intermediate prognosis at diagnosis. We have developed a dual-color, dual-fusion fluorescence in situ hybridization (D-FISH) assay to detect fusion of the MLF1 and NPM1 genes. A blinded investigation was performed using 25 normal bone marrow specimens and 26 bone marrow samples from patients with one or more metaphases with a t(3;5)(q21-q25;q31-q35) or a der(5)t(3;5)(q21-q25;q31-q35) previously identified by chromosome analysis. Once unblinded, the results indicate our D-FISH method identified NPM1/MLF1 fusion in 15 of the 26 fully evaluated patient samples. Excluding three samples with a single abnormal t(3;5) metaphase, 15 of 17 (88%) patient samples with a balanced t(3;5) demonstrated NPM1/MLF1 fusion, and 0 of 6 patient samples with a der(5)t(3;5) demonstrated NPM1/MLF1 fusion, suggesting only the balanced form of this 3;5 translocation as observed by karyotype is associated with NPM1/MLF1 fusion. Overall, the FISH results demonstrated five different outcomes (NPM1/MLF1 fusion, MLF1 disruption, MLF1 duplication, NPM1 deletion, and normal), indicating significant molecular heterogeneity when the 3;5 translocation is identified. The development of this sensitive D-FISH strategy for the detection of NPM1/MLF1 fusion adds to the AML FISH testing repertoire and is effective in the detection of this translocation at diagnosis as well as monitoring residual disease in AML patients.
ASJC Scopus subject areas
- Pathology and Forensic Medicine
- Molecular Medicine