Evaluation of a Prognostic Epigenetic Classification System in Chronic Lymphocytic Leukemia Patients

Abstract

Background: Methylation at 5 CpG sites was previously shown to classify chronic lymphocytic leukemia (CLL) into 3 prognostic subgroups. Here, we aimed to validate the marker set in an additional cohort and to evaluate its clinical utility for CLL patient stratification. Methods: We evaluated this epigenetic marker set in 79 German patients using bisulfite treatment followed by pyrosequencing and classification using a support vector machine-learning tool. Results: The n-CLL, i-CLL, and m-CLL classification was detected in 28 (35%), 10 (13%), and 41 (51%) patients, respectively. Epigenetic grouping was associated with IGHV mutational status (P = 2 × 10−12), isolated del13q (P = 9 × 10−6), del17p (P =.015), complex karyotype (P =.005), VH-usage, and clinical outcome as time to first treatment (P = 1.4 × 10−12) and overall survival (P =.003). Multivariate Cox regression analysis identified n-CLL as a factor for earlier treatment hazard ratio (HR), 6.3 (95% confidence interval [CI] 2.4-16.4; P =.0002) compared to IGHV mutational status (HR 4.6, 95% CI 1.9-11.3, P =.0008). In addition, when comparing the prognostic value of the epigenetic classification system with the IGHV classification, epigenetic grouping performed better compared to IGHV mutational status using Kaplan-Meier estimation and allowed the identification of a third, intermediate (i-CLL) group. Thus, our study confirmed the prognostic value of the epigenetic marker set for patient stratification in routine clinical diagnostics.