Purpose: Ovarian carcinomas are believed to arise de novo from surface epithelium, but the actual molecular pathogenesis is unknown. The aim of this study was to compare the promoter hypermethylation profiles of ovarian epithelial neoplasms to better understand the role of epigenetic silencing in carcinogenesis.
Experimental design: We analyzed the DNA promoter methylation status of eight tumor suppressor and cancer-related genes (p16, RARbeta, E-cadherin,H-cadherin, APC, GSTP1, MGMT, RASSF1A) in 23 benign cystadenomas, 23 low malignant potential (LMP) tumors, and 23 invasive carcinomas by methylation-specific PCR.
Results: Benign cystadenomas exhibited promoter hypermethylation in only two genes, p16 (13%) and E-cadherin (13%). LMP tumors also showed p16 (22%) and E-cadherin (17%) methylation, in addition to RARbeta (9%) and H-cadherin (4%). All eight genes were hypermethylated in invasive cancers at a frequency of 9% to 30%. The mean methylation index was highest in invasive tumors [0.20 versus 0.065 (LMP) and 0.033 (cystadenomas); P = 0.001]. Promoter methylation of at least one gene was most commonly observed among invasive cancers [78% versus 44% (LMP; P = 0.03) and 26% (cystadenomas; P = 0.0009)]. Three genes exhibited higher methylation frequencies in invasive tumors: RASSF1A (30% versus 0%; P = 0.0002), H-cadherin (22% versus 2%; P = 0.013), and APC (22% versus 0%; P = 0.003).
Conclusions: Promoter hypermethylation is a frequent epigenetic event that occurs most commonly in invasive epithelial ovarian carcinomas. The profile of aberrant methylation suggests that an accumulation of events at specific genes may trigger malignant transformation of some benign cystadenomas and LMP tumors.