487 Liquid biopsy for diagnosing ovarian cancer- quantification of cell-free DNA and p53 mutational analysis

Introduction/Background Circulating tumor DNA found in women with malignancy, enters plasma due to lysis of cells at the interface between the primary tumor and the circulation. The primary objective of this study was to isolate and quantify cell-free DNA (cfDNA) from peripheral blood, analyze p53 mutations and correlate with tumor burden in epithelial ovarian malignancy. Secondary objective was to study the degree of agreement between cfDNA p53 mutations and tissue p53 immunohistochemistry. Methodology This prospective case-control study was carried out over 18 months from November 2018 to April 2020 at a tertiary teaching institution. Considering the exploratory nature of the study, study group (n=20) comprised women with epithelial ovarian malignancy. Control groups were women with borderline tumors (n=10) and benign epithelial ovarian tumors (n=10). 58 women who were treatment naive and admitted for surgery entered the study but only those with a final histopathology of epithelial ovarian tumor (malignant, borderline and benign) were included. Peritoneal carcinomatosis index (PCI), surgical complexity score and cytoreductive score was calculated in women undergoing primary cytoreduction. Plasma samples for cfDNA was collected just before surgery and stored at -20oC. cfDNA was extracted from plasma serum using a DNA isolation kit and quantified with Nanodrop Spectrophotometer. ARMS PCR was used to detect a point mutation in Exon 8, codon 239 of p53 using primer pairs. p53 immunostaining was performed on tissue samples using monoclonal antibody directed against p53. Statistical analysis was done using SPSS version 21. Results In women with malignant ovarian cancer isolated cfDNA was highest (1330 ng/mL) in comparison to those with benign or borderline ovarian tumors (748.5 ng/mL and 448.5 ng/mL, respectively) reaching statistical significance, p=0.023. Quantity of cfDNA also correlated well with the histopathological grade of the tumor and stage of the disease, p Analysis of cfDNA p53 mutation in exon 8 showed that 55% of the women diagnosed with malignant ovarian tumor harboured this mutation (p=0.043). Correlation of tissue p53 with cfDNA p53 mutation was statistically significant, p=0.007. All women with malignant ovarian tumor in whom cfDNA p53 mutation was present at codon 239 of exon 8 stained positive for tissue p53 mutation. Conclusion cfDNA p53 mutation in exon 8 was detected at higher frequency in women with malignant epithelial ovarian cancer. Significant correlation was seen between tissue p53 and cfDNA p53 mutation suggesting that mutational analysis of cfDNA could act as biomarker for the diagnosis of ovarian tumors. Disclosures Shalini Rajaram – No conflict of interest Aanchal Verma - No conflict of interest Rajarshi Kar - No conflict of interest Vinod Arora - No conflict of interest Bindiya Gupta - No conflict of interest Sandhya Jain - No conflict of interest