CpG IslandMethylator Phenotype Redefines the Prognostic Effect of t(12;21) in Childhood Acute Lymphoblastic Leukemia

Purpose: 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. Experimental Design: Methylation-specific PCRwas used to analyze themethylation status of 38 genes involved in cell immortalization and transformation in 54 ETV6/RUNX1-positive samples in comparison with190 ETV6/RUNX1-negative samples. Results: 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 =0.002andP = 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, andP73) showed specificity for ETV6/RUNX1-positive subset of samples. Conclusion: Our results suggest that methylation profile may be a potential new biomarker of risk prediction in ETV6/RUNX1-positive acute lymphoblastic leukemias.