RASSF1A promoter methylation in high-grade serous ovarian cancer: A direct comparison study in primary tumors, adjacent morphologically tumor cell-free tissues and paired circulating tumor DNA.

Lydia Giannopoulou,Sabine Kasimir-Bauer,Kitty Pavlakis,Evi S Lianidou,Issam Chebouti

doi:10.18632/oncotarget.15249

Abstract

The RASSF1A promoter is frequently methylated in high-grade serous ovarian cancer (HGSC). We examined RASSF1A promoter methylation in primary tumors, adjacent morphologically tumor cell-free tissues and corresponding circulating tumor DNA (ctDNA) samples of patients with HGSC, using a real-time methylation specific PCR (real-time MSP) and a methylation-sensitive high-resolution melting analysis (MS-HRMA) assay for the detection and semi-quantitative estimation of methylation, respectively. Two groups of primary HGSC tumor FFPE samples were recruited (Group A n=67 and Group B n=61), along with matched adjacent morphologically tumor cell-free tissues (n=58) and corresponding plasma samples (n=59) for group B. Using both assays, RASSF1A promoter was found highly methylated in primary tumors of both groups, and at lower percentages in the adjacent morphologically tumor cell-free tissues. Interestingly, RASSF1A promoter methylation was also observed in ctDNA by real-time MSP. Overall survival (OS) was significantly associated with RASSF1A promoter methylation in primary tumor samples using MS-HRMA (P=0.023). Our results clearly indicate that RASSF1A promoter is methylated in adjacent tissue surrounding the tumor in HGSC patients. We report for the first time that RASSF1A promoter methylation provides significant prognostic information in HGSC patients.

Highlights

Ovarian cancer represents the third most frequent gynecological cancer and the fifth leading cause of cancerrelated death in women [1]
We report for the first time that RASSF1A promoter methylation provides significant prognostic information in high-grade serous ovarian cancer (HGSC) patients
We further evaluated the percentages of RASSF1A promoter methylation in primary tumor samples and adjacent tissues, by using the semi-quantitative MSHRMA assay

Summary

Introduction

Ovarian cancer represents the third most frequent gynecological cancer and the fifth leading cause of cancerrelated death in women [1]. Epithelial ovarian cancer is the main type, characterized by histological and molecular heterogeneity. It is clear that epigenetic alterations hold an important role in cancer initiation and progression and that aberrant DNA methylation, especially promoter hypermethylation of tumor suppressor genes is a frequent event in most human cancers [9]. Epigenetic inactivation of a tumor suppressor gene often results from its promoter methylation and is considered as an early event www.impactjournals.com/oncotarget during carcinogenesis [10]. Many studies have reported methylation changes in epithelial ovarian cancer [11] and a recent review summarizes the differences in the observed methylation patterns in the main histological subtypes of the disease, including HGSC [12]

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