NDRG4 and breast neoplasm: Next, we performed in silico expression and methylation analysis using paired normal and primary breast tumors obtained from The Cancer Genome Atlas (TCGA) through the MethHC database.23 On average, tumor samples exhibited higher levels of DNA methylation in the NDRG4 promoter region (−1500 to +500 relative to TSS) than their normal counterparts (Fig. 2a, p < 0.001).17 Accordingly, we categorized the TCGA tumor samples into four classes (Q1–Q4) according to NDRG4 promoter methylation quartiles.