Combining cytogenetic and epigenetic approaches in chronic lymphocytic leukemia improves prognosis prediction for patients with isolated 13q deletion.

Background: Both defective DNA methylation and active DNA demethylation processes are emerging as important risk factors in chronic lymphocytic leukemia (CLL). However, associations between 5-cytosine epigenetic markers and the most frequent chromosomal abnormalities detected in CLL remain to be established.

Methods: CLL patients were retrospectively classified into a cytogenetic low-risk group (isolated 13q deletion), an intermediate-risk group (normal karyotype or trisomy 12), and a high-risk group (11q deletion, 17p deletion, or complex karyotype [≥ 3 breakpoints]). The two 5-cytosine derivatives, 5-methylcytosine (5-mCyt) and 5-hydroxymethylcytosine (5-hmCyt), were tested by ELISA ( n  = 60), while real-time quantitative PCR was used for determining transcriptional expression levels of DNMT and TET ( n  = 24).

Results: By using global DNA methylation/demethylation levels, in the low-risk disease group, two subgroups with significantly different clinical outcomes have been identified (median treatment-free survival [TFS] 45 versus > 120 months for 5-mCyt, p  = 0.0008, and 63 versus > 120 months for 5-hmCyt, p  = 0.04). A defective 5-mCyt status was further associated with a higher percentage of 13q deleted nuclei (> 80%), thus suggesting an acquired process. When considering the cytogenetic intermediate/high-risk disease groups, an association of 5-mCyt status with lymphocytosis ( p  = 0.0008) and the lymphocyte doubling time ( p  = 0.04) but not with TFS was observed, as well as a reduction of DNMT3A , TET1 , and TET2 transcripts.

Conclusions: Combining cytogenetic studies with 5-mCyt assessment adds accuracy to CLL patients' prognoses and particularly for those with 13q deletion as a sole cytogenetic abnormality.