Since their initial discovery, TET2
mutations have been extensively studied in MPN and MDS, and reports involving patients with AML2–4,7,12,42
have often focused on secondary AML arising from these disorders. In contrast, little is known about the prevalence and clinical relevance of TET2
mutations in primary AML. In two relatively small studies,1,11 TET2
mutations were found in 17% and 19% of patients with primary AML with various karyotypes and 22% of patients with CN-AML.11
In our larger cohort, the prevalence of TET2
mutations in primary CN-AML was 23%. Our findings that most TET2
mutations are frame shift or nonsense changes (likely resulting in a truncated protein) and that missense mutations cluster in two evolutionarily conserved domains of TET2
are in agreement with previous MDS and MPN series.1,2,5,12
We analyzed matched germline DNA samples to ascertain the somatic nature of sequence changes. In our cohort, all evaluable missense changes outside the two conserved domains were germline variants and thus likely nonpathogenic. Therefore, patients carrying these variations were excluded from our analyses.
We focused on patients with CN-AML because the prognosis of this cytogenetic subset is affected by molecular markers that are increasingly used for prognostication and risk-adapted management decisions.14–16,23–27
We demonstrated that TET2
mutations are associated with older age (as reported for MPN5
) and higher pretreatment WBC and that they rarely occur together with IDH1
mutations. Consistent with our previous report27
that mutations of IDH2
codon R172 are mutually exclusive with other gene mutations in CN-AML, no patient concurrently harbored a TET2
mutation and an IDH2
To the best of our knowledge, our study is the largest report on the prognostic implications of TET2
mutations in primary CN-AML. Nibourel et al,11
who focused on patients achieving CR, found no differences in DFS or OS between 12 TET2
-mutated and 42 TET2
-wt patients with CN-AML. In another study3
of 93 patients with primary or secondary AML, TET2
mutations were associated with inferior OS, but this analysis did not consider cytogenetics or other potentially confounding variables.
With a growing number of gene mutations being identified in CN-AML, it becomes increasingly important to consider individual markers in their genetic context. The prognostic impact of one mutation may vary depending on the presence or absence of other molecular markers (eg, NPM1
mutations are associated with favorable outcomes particularly in the absence of FLT3
For clinical decision making, risk stratification algorithms integrating prognostic information conveyed by a panel of molecular markers are needed. Recently, the ELN proposed a risk stratification scheme for AML based on cytogenetics and three established molecular prognostic markers.16
The relative prognostic importance of novel molecular markers should not only be evaluated in multivariable models but also needs to be investigated in the context of accepted classification systems. This approach allows judging the potential of new markers to be readily applicable in the clinic and to be incorporated in risk-adapted management decisions for patients with AML.
The ELN classification categorizes patients with CN-AML into a favorable-risk group (CEBPA
-mutated and/or mutated NPM1
-ITD; ≈ 45% of patients with CN-AML14
) and a less-favorable intermediate-I–risk group (all remaining patients with CN-AML). To examine whether TET2
mutations can be used to improve this widely accepted classification, we studied their prognostic value within the ELN risk categories of CN-AML. Among ELN favorable-risk patients, those with TET2
mutations had lower response rates and a higher risk of relapse or death than TET2
-wt patients. The favorable-risk category comprises two molecularly defined subgroups of CN-AML: CEBPA
-mutated patients and those with mutated NPM1
-ITD. Notably, when separately evaluating these two genotypes, we found that TET2
mutations were associated with inferior outcomes in both subgroups (Data Supplement). In contrast, we observed no significant prognostic impact of TET2
mutations in the ELN intermediate-I–risk category or any of its molecular subsets (Data Supplement), although some of these exploratory subgroup analyses were limited by small sample sizes.
Our study included patients across a broad range of ages, potentially introducing bias in our survival analyses. However, in multivariable analyses adjusting for age group and other variables, TET2
mutations remained associated with inferior EFS, lower CR rates, and shorter DFS among favorable-risk patients. FLT3
, and CEBPA
mutations do not appear in our multivariable models as individual variables, since they are already incorporated in the definition of the ELN risk categories. We did not separately consider FLT3
-ITD:wt allelic ratio because the ELN favorable-risk group included only 19 patients with FLT3
-ITD (all CEBPA
-mutated) and because the adverse impact of a high allelic ratio has been found in younger, but not in older patients.45
Along with TET2 mutations, WT1 mutations were associated with shorter EFS and DFS after adjustment for ELN risk category and other covariables. In our model for CR rate, TET2 mutations were the only gene mutations providing additional prognostic information beyond ELN risk category. To the best of our knowledge, our study is the first to evaluate a novel molecular marker in CN-AML in the context of the current ELN classification and to suggest that TET2 (and possibly WT1) mutations are candidate markers for a refined CN-AML classification scheme.
The function of the TET2 protein is not fully understood. Its paralogue TET1 was recently shown to catalyze conversion of 5-methylcytosine to 5-hydroxymethylcytosine in mammalian DNA, suggesting a role of TET proteins in epigenetic regulation.46,47
To gain insights into the biologic consequences of TET2
mutations, we studied genome-wide gene- and microRNA-expression signatures. Among favorable-risk patients, we identified a TET2
mutation-associated gene-expression signature comprising 136 differentially expressed named genes. TET2
mutations were associated with deregulation of genes involved in stem-cell self-renewal, cell cycle control, and cytokine and growth factor signaling, which may help explain their adverse prognostic impact. In contrast, no significant gene-expression signature could be identified in the intermediate-I–risk cohort.
MicroRNA-expression profiling revealed distinct TET2 mutation-associated signatures in both the favorable-risk and intermediate-I–risk groups, involving several microRNAs implicated in CN-AML and other hematologic malignancies. Interestingly, the microRNA-expression signatures in the two ELN risk groups did not overlap. Apparently, TET2 mutations affect different sets of microRNAs and genes in favorable-risk and intermediate-I–risk patients with CN-AML. These differences show that the ELN classification identifies distinct biologic subsets of CN-AML and corresponds to our finding that the prognostic impact of TET2 mutations also varies between the two ELN risk categories. Together, our results suggest that the biologic and clinical consequences of TET2 mutations in CN-AML differ between the ELN risk groups, although the mechanisms underlying this differential impact remain unclear.
In conclusion, TET2
mutations occur in > 20% of adult patients with primary CN-AML and may be useful for improving genetic risk classification schemes, such as the ELN classification, which are increasingly used in the clinic to guide personalized treatment decisions. The current ELN guidelines generally do not recommend allogeneic transplantation for favorable-risk patients in first CR,16
and none of our patients received such treatment as postremission therapy. However, our results suggest that a subset of these patients, identified by mutated TET2
, do not do well with conventional postremission treatment. If our results are corroborated, some of these patients might be considered candidates for alternative therapeutic approaches.