Clinical Significance of FLT3/ITD and NPM1 Mutation in Acute Myeloid Leukemia (AML).

Acute myeloid Leukemia(AML) is known as heterogeneous disease, especially in adult AMLs. FLT3/ITD and NPM1 mutation are frequentry seen at the same time, and expected as a role of stratification factor. FLT3/ITDs are the most frequent genetic alterations in AML, found in approximately 20% of adult AMLs. FLT3/ITD is associated with leukocytosis and worse prognoses. ITD mutations vary in size and location, ranging in size from 3 to hundreds of nucleotides. Recently, it is reported that nucleophosmin gene(NPM1) is mutated in a high proportion of gene(NPM1) is mutated in a high proportion of adults with AML and associated with a normal karyotype and FLT3 mutations. In this study, we examined prognostic significance of FLT3/ITD and NPM1 mutation in de novo adult AMLs. We analyzed 51 AML patients(median age:48y/o, range:17–83y/o). Mainly almost patients underwent JALSG AML97 protocol therapy. Acute promyelocytic leukemia was also comprised in this analysis, and 18 of 54 cases were underwent bone marrow transplantation(BMT). Genomic DNA was amplified by means of a polymerase chain reaction, and agarose gel elecrophoresis was used for detection of ITD mutation. ITD size was determined by sequencing analysis. For NPM1 mutation detection, we amplified genomic DNA by PCR using primers as previously reported. We found 11(22%) patients with FLT3/ITD mutation. ITDs were associated with higher WBC count(median of 90.7×10⁹/L versus 5.85×10⁹/L; p<.005) and higher peripheral blast percentage(median of 60% versus 39%; p=.016). OS was somewhat poorer for ITD positive patients compared with ITD negative patients(p=.12). FLT3/D835 mutations were found in 2(4%) of 51 patients. There was no case that had both FLT3/ITD and FLT3/D835 mutations. We next examined whether ITD size had an impact on clinical outcomes. ITD size was detectable in 9 out of 11 cases. Median ITD size was 33bp(range, 21–75bp). FLT3/ITD size was not significantly correlated with WBC count(p=.905), marrow(p=.730) or peripheral blast percentage(p=.413). Then we classified these FLT3/ITD mutations into long(≥40bp;4 cases) and short ITD(<40bp; 5 cases). Previous study pointed out that increasing ITD size might be associated with OS or RFS, but in this study we didn’t find that increasing ITD size was not associated with OS(p=.71). ITD size was not significantly correlated with NPM1 mutations. NPM1 mutations were found in 7(14%). Normal karyotype were found in 5(71%). Both FLT3/ITD and NPM1 mutation were found in 3 patients,a nd all died in early clinical courses. Previous reports pointed that NPM1 mutation was a favorable prognostic factor for overall survival(OS), but in this study, 5 year OS was 14% and worse compared to other studies. In FLT3/ITD positive case, statistical significance were not shown with or without NPM1 mutation(p=0.74). FLT3/ITD and NPM1 dual positive cases seems to be very poor prognosis, and intensive or aggressive therapy plans including allo bone marrow transplantation are needed for improving prognosis.