Previous studies have indicated that DNA methylation plays a significant role in the downregulation of mRNA expression, with the low levels of many tumour suppressor genes' mRNAs attributed to the hypermethylation of the CpG islands in their promoter regions, such as p16, Rb, PTEN, ZNF154 and BRCA1.10, 11, 12, 15, 16, 17, 18, 19, 20. This evidence concerns the gene RB1 and neoplasm.