Gene Mutations in Paired Initial Presentation and Relapse Samples From Acute Myeloid Leukemia Patients,

Gene mutationswere found in acute myeloid leukemia (AML) and their importance has been noted. Flt3, NPM1 and CEBPA were detected in “intermediate cytogenetic risk” group, and are becoming possible to distinguish subsets of patients with different outcomes. Moreover, several groups have reported that these mutations would be useful for not only predictive markers, but also minimal residual disease (MRD) markers in AML. Several recent studiesprovided compelling evidence that mutations in epigenetics modifying genes contribute to AML pathogenesis. DNMT3a mutations were common (about 20% frequency) in de novo AML and associated with poor prognosis. Furthermore, mutations of IDH1/2 and TET2 that also seem to be collaborating on DNA methylation modifying are detected, too.

To clarify the importance and dynamics of these mutations in clinical course, we examined Flt3, NPM1, CEBPA, DNMT3a and IDH1/2 gene mutations in paired samples at initial presentation and relapse of AML patients.

We analyzed the samples from adultpatients with de novo AML diagnosed at Nippon Medical School Hospital from 2000 to 2010. Mutation analyses were performed for Flt3 ITD by PCR amplification, Flt3 TKD by PCR-RFLP, and NPM1, CEBPA, IDH1/2 and DNMT3a mutations by direct sequence.

The 31 AML patients were enrolled. In chromosomal analysis at initial presentation, 19 with normal karyotype (NK-) AML, 2 with trisomy8, 4 with 11q23 associated, 1 with monosomy7, 2 with complex karyotypes and 3 with non-specific aberrations were observed. 15 cases were comparable for paired samples at diagnosis and relapse. 13 of them (86.7%) showed additional chromosomal aberrations at relapse.

Gene mutations were detected more frequently in cytogenetic intermediate risk group (83.3%) than poor risk group (0%). There were 11 patients with Flt3 ITD at initial presentation, but 3 of them had no detectable mutation at relapse. Flt3 TKD were found in 3 patients at initial presentation, but all of them were lost at relapse. Among 12 patients with NPM1 mutation at initial presentation, 3 of them lost their mutation at relapse. CEBPA mutation was detected in only one paired sample at diagnosis and relapse. DNMT3a mutations were detected in 8 patients both at initial presentation and relapse. IDH2 mutations were detected in two patients at initial presentation, but 1 of them was lost at relapse. In summary, of the 37 gene mutations at initial presentation, 10 gene mutations were lost at relapse, and only 1 acquired gene mutation was detected at relapse. Flt3 ITD, NPM1, DNMT3a and IDH2 mutations frequently coexisted with another mutation.

This study is the first report of consecutive analyses on the major gene mutations in AML. Newly acquired gene mutations at relapse are rare compared to frequent additional chromosomal aberrations at relapse.

Flt3 ITD mutations at initial presentation were detected also at relapse. This finding indicates that Flt3 ITD are responsible for relapse and refractoriness. On the other hand, all 3 cases with Flt3 TKD lost the mutation at relapse, suggesting that Flt3 TKD mutation does not contribute to their relapse.

Some of Flt3 ITD, Flt3 TKD and NPM1 mutations could not be detected at relapse, indicating that these mutations should be used carefully for MRD marker. DNMT3a mutations were detected both at diagnosis and relapse in all 8 cases. This finding suggests that DNMT3a mutations might be a useful MRD marker.

No relevant conflicts of interest to declare.