Liquid biopsy for diagnosing epithelial ovarian cancer: quantification of cell-free DNA and p53 mutational analysis
To isolate and quantify cell-free DNA, analysis for p53 mutations, and correlation with tumor burden in women with epithelial ovarian cancer compared with benign and borderline epithelial ovarian tumors. In this case-control study, plasma samples of eligible women collected 1 hour before surgery and based on final histopathology, women with epithelial ovarian cancer recruited as cases and borderline, and benign ovarian tumors as controls. Cell-free DNA extracted from plasma serum and quantified using Nanodrop Spectrophotometer. Amplification refractory mutation system-based polymerase chain reaction was used to detect point mutation in exon 8, codon 239 of p53 using primer pairs. p53 immunostaining was performed on tissue samples. A total of 40 women (20 cases of epithelial ovarian cancer and 10 each of benign and borderline ovarian tumors [controls]) were included in a 2:1:1 ratio. The mean cell-free DNA amount was 1330 ± 1705.4 ng/mL in women with epithelial ovarian cancer compared with 748.5 ± 444.8 and 448.5 ± 203.9 ng/mL in benign and borderline ovarian tumors, respectively (p = .023). In those with high-grade serous ovarian cancer, it was 2640 ± 2450.6 ng/mL compared with 600 ± 316.7 and 652.5 ± 158.9 ng/mL in low-grade serous and mucinous ovarian cancer, respectively (p = .006). In stage I and II ovarian cancer, these were 502.5 ± 134.4 and 330 ± 296.9 ng/mL, respectively, compared with 1655 ± 1924.8 ng/mL in stage III disease (p = .004). A total of 11 (55%) women with epithelial ovarian cancer harbored mutation in exon 8, codon 239 of p53 compared with 2 (20%) each in benign and borderline ovarian tumors (p = 0.07). Fair agreement was noted between cell-free DNA p53 mutation and abnormal tissue p53 staining on immunohistochemistry (κ = 0.41). Cell-free DNA amount was higher in women with epithelial ovarian cancer than women with benign and borderline ovarian tumors, with higher levels in advanced stage and high-grade serous carcinoma sub-type. Cell-free DNA p53 mutational analysis yielded fair concordance with tumor tissue p53 immunohistochemical results.