Aberrant Methylation during Cervical Carcinogenesis

We studied the pattern of aberrant methylation during the multistage pathogenesis of cervical cancers. We analyzed a total of 73 patient samples and 10 cervical cancer cell lines. In addition, tissue samples [peripheral blood lymphocytes ( n = 10) and buccal epithelial cells ( n = 12)] were obtained from 22 healthy volunteers. On the basis of the results of preliminary analysis, the cervical samples were grouped into three categories: ( a ) nondysplasia/low-grade cervical intraepithelial neoplasia (CIN; n = 37); ( b ) high-grade CIN ( n = 17); and ( c ) invasive cancer ( n = 19). The methylation status of six genes was determined ( p16, RAR β, FHIT, GSTP1, MGMT , and hMLH1 ). Our main findings are as follows: ( a ) methylation was completely absent in control tissues; ( b ) the frequencies of methylation for all of the genes except hMLH1 were >20% in cervical cancers; ( c ) aberrant methylation commenced early during multistage pathogenesis and methylation of at least one gene was noted in 30% of the nondysplasia/low-grade CIN group; ( d ) an increasing trend for methylation was seen with increasing pathological change; ( e ) methylation of RAR β and GSTP1 were early events, p16 and MGMT methylation were intermediate events, and FHIT methylation was a late, tumor-associated event; and ( f ) methylation occurred independently of other risk factors including papillomavirus infection, smoking history, or hormone use. Although our findings need to be extended to a larger series, they suggest that the pattern of aberrant methylation in women with or without dysplasia may help identify subgroups at increased risk for histological progression or cancer development.