Supervised hierarchic clustering of 187 paired breast cancer samples by using methylation data from selected genes in the validation study. (a) Heat map and clustering of significant (FRD-corrected, P < 0.01) differences between tumors (red) and adjacent tissues (green). Heat-map colors symbolize DNA methylation, as indicated in the color key. (b) Principal component analysis (PCA) plots showing separation between tumor and adjacent tissue. (c) Box plots showing lower methylation density in adjacent tissue compared with tumors.