Lidocaine, which was presented in time and dose dependency, could increase the demethylation of breast cancer cells, and the methylation-inhibiting effect of DAC (5-azacytidine), which is a kind of DNMTs (DNA methyltransferases), could decrease the CpG (CpG island) methylation of tumor suppressor genes—RARβ and RASSF1A, and increase the sensitivity of cisplatin to breast cancer cells (97, 98). The gene discussed is RASSF1; the disease is breast cancer.