The Investigation of Molecular Markers in the Prognostically Intermediate Karyotype Group in AML Provides Clinically Relevant Information.

Acute myeloid leukemia (AML) can be divided into prognostically different subgroups based on chromosomal aberrations. However, more than 50% of AML have no karyotype changes or those with yet unknown prognostic significance and they are usually pooled together into the prognostically intermediate karyotype group (I-AML). Here we approached the subclassification of this large AML group by molecular markers. Six genes were screened for mutations and analyzed for their prognostic significance in comparison to cases without the respective mutation. Results of this analysis are given in the table. Significant unfavorable impact on OS was shown for the MLL-PTD in the total group and for AML1 mutations in FAB M0. EFS and RFS was adversely affected by the FLT3-LM and EFS in AML1 mutated cases. In contrast CEBPA mutations disclose a favorable subgroup. Molecular mutations are not mutually exclusive. At least one additional mutation was observed in all possible combinations in 1.1% to 34.7% (mean 10.9%). The most frequent combinations are MLL-PTD + FLT3-LM in 34.7% of all MLL-PTD+ cases and CEBPA+FLT3-LM in 34.4% of all CEBPA+ cases. In contrast, double mutations of FLT3 or combinations of FLT3 or KIT with NRAS are rare (1.1%–3.6%), suggesting a better cooperativity of CEBPA and MLL-PTD with FLT3-LM. For all combinations an effect on prognosis could not be shown in addition to those given in the table. Three mutations were detected in 6 cases and again all of the possible genes were involved at least once. In only one third of all I-AML patients none of the analyzed mutations was detected. A two step hypothesis has recently been postulated for AML with fusion transcripts. The presented data support a two or maybe multistep theory for mutagenesis in AML with normal karyotype. Molecular mutations may have less transforming capacity, so that more than two mutations have to be accumulated. The pattern of the detected mutations suggests CEBPA and MLL-PTD to be type II mutations (differentiation) whereas FLT3, KIT, and RAS have previously postulated to be type I mutations (proliferation). In addition, gene expression studies were performed in 228 I-AML positive for one or more of the mutations. All of the different mutation groups did not reveal distinct individual expression patterns. This suggests that specific pathways may be involved in the normal karyotype AML that are triggered redundantly by different gene mutations.

Prognostic significance of gene mutations compared to the group tested negative for this mutation in the prognostically intermediate group