Clinical relevance of internal tandem duplication of the FLT3 gene in childhood acute myeloid leukemia.

BACKGROUND: Recently, an internal tandem duplication of the FLT3 gene (FLT3/ITD) was found in approximately 20% of adult acute myeloid leukemia (AML) cases and associated with a poor outcome. However, there are few studies on FLT3/ITD in childhood AML, and the clinical significance of FLT3/ITD is thus unclear.

METHODS: FLT3/ITD was analyzed in 80 children with de novo AML. The genomic DNA polymerase chain reaction (PCR) assay was performed to identify FLT3/ITD. Genescan analysis to determine the allelic distribution was then performed for those PCR products with aberrant bands. Direct sequencing of PCR products was also carried out in each sample with FLT3/ITD.

RESULTS: The incidence of FLT3/ITD was 11.3% (9 out of 80 patients) in AML, with 25% (3 out of 12 patients) in acute promyelocytic leukemia (APL) and 8.8% (6 out of 68 patients) in non-M3 AML. The size of duplicated fragments varied from 21 base pairs (bp) to 75 bp, and the mutant to wild type ratio of FLT3 ranged from 0.28 to 16.60 in the nine patients with FLT3/ITD. The incidence of FLT3/ITD in childhood AML in patients > 10 years of age was 24%, compared to 5% of those patients
CONCLUSIONS: The current study shows that the mutant FLT3 to wild type ratio, but not the presence of FLT3/ITD itself, may serve as a potential marker to improve risk-assessment in childhood AML.