Background: Specific tumour suppressor genes with promoter methylation in ovarian clear cell adenocarcinoma (OCCA) can be one important epigenetic mark distinguishing OCCA from ovarian serous adenocarcinoma (OSA), benign endometriotic cysts and normal ovarian epitheliums.
Materials and methods: Five OCCA cell lines, 63 cancer tissues (48 OCCA and 15 OSA), 10 benign endometriotic cysts and five normal ovarian epitheliums were analysed by methylation-specific PCR using pooled DNAs to determine the methylation status of the promoter of the target genes, including genes for secreted frizzled-related proteins (sFRP1 to 5), adenomatous polyposis coli (APC), retinoblastoma protein 1 (Rb1), breast cancer 1 gene (BRCA1), p14(ARF), p15(INK4b), p16(INK4a) and survivin. Methylation frequencies of identified targets were further analysed with individual DNA samples.
Results: The sFRP5 promoter was significantly methylated in all OCCA cell lines, with 64.6% in OCCA tissues compared with 13.3% in OSA, and 0% in benign endometriotic cysts and normal ovarian epitheliums (P < 0.0001). With a median follow-up of 44 months, the expected 5-year overall survival (OS) for patients with methylated sFRP5 promoter were significantly worse than for those with unmethylated sFRP5 (52% vs. 88%, P = 0.03). After adjusting for age, stage, and residual disease after primary surgery, patients with unmethylated sFRP5 promoter had an independent good prognostic factor in OS (P = 0.017).
Conclusion: The high percentage of promoter methylation in the sFRP5 gene in OCCA indicates its importance in the development of OCCA and is a potential useful marker for prognoses and target for treatment of OCCA.