Abstract 442: RASSF1A gene promoter methylation in primary tumors, adjacent morphologically normal tissues and plasma samples of patients with high grade serous ovarian cancer

Abstract

Abstract Introduction: RASSF1A promoter methylation is frequent in high grade serous ovarian cancer (HGSC), the most common histological subtype. We examined RASSF1A promoter methylation in primary tumors, adjacent normal tissues and corresponding plasma samples of patients with HGSC, using real-time methylation specific PCR (real-time MSP) and methylation-sensitive high-resolution melting analysis (MS-HRMA). Materials and methods: A training group of 78 primary HGSC FFPEs was first analyzed using both real-time MSP and MS-HRMA. Our validation group consisted of 61 primary HGSC FFPEs, 58 adjacent tissues (analyzed using both real-time MSP and MS-HRMA), and 59 corresponding plasma samples (analyzed using real-time MSP). The specificity of both assays was evaluated by analyzing a group of 16 fallopian tube samples from healthy individuals. OVCAR29 and IGROV1 cell lines were used as positive controls. Results: In the training group, RASSF1A promoter methylation was detected in 33/78 (42.3%) by real-time MSP and in 33/78 (42.3%) by MS-HRMA (Agreement = 94.9%, P = 0.001, k = 0.895). The validation group results are shown in Table 1. According to the semi-quantitative MS-HRMA, RASSF1A promoter methylation was detected at significantly lower percentages in the adjacent morphologically normal tissues, compared to the paired primary tumors. In corresponding plasma samples, methylation was detected in 15/59 (25.4%) (Agreement with paired tumors = 60.7%, P = 0.259, k = 0.143). Both real-time MSP and MS-HRMA revealed no RASSF1A promoter methylation in the small group of normal fallopian tubes (n = 16). Conclusion: RASSF1A promoter is highly methylated in primary tumors and at lower percentages in the adjacent normal tissues. In all cases, MS-HRMA gave comparable results with real-time MSP. Evaluation of the clinical significance of RASSF1A promoter methylation in corresponding plasma requires further investigation. Table 1RASSF1A promoter methylationMethodPrimary tumor samples (validation group) N = 61Adjacent tissues N = 58Agreement (paired samples, N = 57)Real time MSP25/61 (41%)17/58 (29.3%)48/57(84.2%), P = 0.001, k = 0.652MS-HRMA28/61 (45.9%)21/58 (36.2%)51/57(89.5%), P = 0.001, k = 0.782Agreement (methods)58/61(95.1%), P = 0.001, Cohen's kappa = 0.90050/58(86.2%),P = 0.001, Cohen's kappa = 0.689 Citation Format: Lydia Giannopoulou, Issam Chebouti, Kitty Pavlakis, Sabine Kasimir-Bauer, Evi S. Lianidou. RASSF1A gene promoter methylation in primary tumors, adjacent morphologically normal tissues and plasma samples of patients with high grade serous ovarian cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 442.