Genes prone to hypermethylation in cancer are not constitutively expressed. (a) Hypermethylation-prone and -resistant genes are associated with distinct biological processes. Shown are graphs of the percent enrichment or depletion for the 10 most enriched GO biological process in the hypermethylation resistant and prone gene sets. For each term the enrichment or depletion in both gene sets is plotted. All terms were enriched or depleted to a significant level for both gene sets (Fisher's exact tests, P < 0.05). (b) Hypermethylation prone genes are tissue-specific. Histograms show the distribution of tissue-specificity scores observed for hypermethylation prone and resistant genes. Specificity scores for prone and resistant gene sets were compared using a Wilcoxon rank sum test. (*** P < 0.001). GO, genome ontology.