SRA

Triple negative breast cancers (TNBCs) comprise a heterogeneous group of cancers with varying prognoses, presenting a challenge for effective clinical management. Epigenetic alterations in the cancer methylome are common in breast cancer and provide novel options for tumor stratification on the basis of prognosis. Advances in genome-wide DNA methylation technology have enabled more comprehensive identification of potential epigenetic diagnostic and prognostic cancer biomarkers. Here, we use MBDCap-Seq to perform genome-wide DNA methylation profiling from archival TNBC and matched normal DNA samples. We identified 822 differentially methylated regions (DMRs) comprising 308 genes affected by cancer-specific promoter hypermethylation. Notably, 51 of these genes are also recurrently mutated in breast cancer, seven of which include members of the axon guidance pathway recently implicated in tumor initiation and progression. Using TCGA methylation data as an independent validation cohort for TNBCs (n= 73), we showed that 36 genomic regions were specific for TNBCs, including both promoter and gene body hypermethyled loci. Importantly, we stratified TNBCs into three distinct methylation clusters associated with better or worse prognosis. Furthermore, we identified a “survival” methylation signature consisting of 17 DMRs that show strong regional association with overall survival, 16 of which overlap DNase1 hypersensitive sites. Notably three of these “survival” DMRs are located in the bi-directional promoter and gene bodies of WT1 gene and its anti-sense counter-part WT1-AS. Together, our data identifies for the first time a cancer DNA methylation diagnostic and prognostic signature that promises to stratify TNBCs for more personalized management. Overall design: Genome-wide methylation profiling of 19 TNBC tumor and 6 matched normal samples was carried out with MBDCap-Seq. In addition, fully methylated control sample was profiled to identify regions of the genome assayable by the MBDCap-Seq technology.