Compared with somatic cells, cancer cells are hypermethylated in the promoter regions of multiple cancer suppressor genes (e.g. MGMT, CdH1, E-cadherin, BRCA1) which is considered a common regulator of transcriptional silencing of tumor suppressor genes, while hypomethylation is observed in the whole genome of cancer cells and is associated with upregulated expression of proto-oncogenes (such as cyclinD2, PAX2, PAX2, and ABCB1) (33, 34). The gene discussed is ABCB1; the disease is cancer.