CpG island methylator phenotype redefines the prognostic effect of t(12;21) in childhood acute lymphoblastic leukemia.

To examine cancer genes undergoing epigenetic inactivation in a set of ETV6/RUNX1-positive acute lymphoblastic leukemias in order to define the CpG island methylator phenotype (CIMP) in the disease and evaluate its relationship with clinical features and outcome. Methylation-specific PCR was used to analyze the methylation status of 38 genes involved in cell immortalization and transformation in 54 ETV6/RUNX1-positive samples in comparison with 190 ETV6/RUNX1-negative samples. ETV6/RUNX1-positive samples had at least one gene methylated in 89% of the cases. According to the number of methylated genes observed in each individual sample, 20 patients (37%) were included in the CIMP- group (0-2 methylated genes) and 34 (67%) in the CIMP+ group (>2 methylated genes). Remission rate did not differ significantly among either group of patients. Estimated disease-free survival and overall survival at 9 years were 92% and 100% for the CIMP- group and 33% and 73% for the CIMP+ group (P = 0.002 and P = 0.04, respectively). Multivariate analysis showed that methylation profile was an independent prognostic factor in predicting disease-free survival (P = 0.01) and overall survival (P = 0.05). A group of four genes (DKK3, sFRP2, PTEN, and P73) showed specificity for ETV6/RUNX1-positive subset of samples. Our results suggest that methylation profile may be a potential new biomarker of risk prediction in ETV6/RUNX1-positive acute lymphoblastic leukemias.