5-Hydroxymethylcytosine correlates with epigenetic regulatory mutations, but may not have prognostic value in predicting survival in normal karyotype acute myeloid leukemia

Stem cells display remarkably high levels of 5-hydroxymethylcytosine (5hmC). Both TET2 and IDH1/2 mutations can impair the production of 5hmC, thus decreasing 5hmC levels. TET2 or IDH1/2 mutations are commonly observed in acute myeloid leukemia (AML). However, the implications of 5hmC on survival in normal karyotype AML patients have not been fully evaluated. The 5hmC levels were analyzed in 375 patients using ELISA. The levels of 5hmC in DNA samples were converted to a log scale for the analysis and correlations with TET2 and/or IDH1/2 mutations were evaluated. The median 5hmC level was 0.065% (range 0.001-0.999). Mutation rates were 13.1% for TET2(mut), 6.7% for IDH1(mut), and 13.9% for IDH2(mut). The prevalence of TET2 and/or IDH1/2 was 33.1% (124/375). TET2 and IDH1/2 mutated patients had significantly lower levels of log(5hmC) compared with patients without TET2 or IDH1/2 mutations (p<0.001). With a median follow-up of 55.5 months (range, 0.7-179.8), there was no significant difference in overall survival, event-free survival, and relapse risk according to TET2(mut) or IDH1/2(mut) (all, p>0.05). To identify its prognostic value, we sub-classified the levels of 5hmC into tertiles for 5hmC values. However, there was no significant association between the categories of 5hmC levels and survival or relapse risk (all p>0.05). Patients with TET2 or IDH1/2 mutations had lower levels of 5hmC. The 5hmC levels may not be predictive of survival in patients with normal karyotype AML.