Plasma cell-free DNA in ovarian cancer: an independent prognostic biomarker

Abstract

Background: Cell-free DNA reflects both normal and tumor-derived DNA released into the circulation through cellular necrosis and apoptosis. The authors sought to determine the role of preoperative total plasma cell-free DNA levels in predicting clinical outcome in patients with ovarian cancer.

Methods: After institutional review board consent, DNA was extracted from plasma of 164 women with invasive epithelial ovarian carcinoma (EOC), 49 with benign ovarian neoplasms, and 75 age-matched controls. The samples were randomly divided into training (n = 144) and validation (n = 144) sets. Quantification of cell-free DNA was performed using real-time polymerase chain reaction for beta-globin, and the number of genome equivalents (GE) per milliliter of plasma was determined. Cell-free DNA was correlated with clinicopathologic parameters.

Results: The training and validation sets were similar in terms of demographic features. In the training set, EOC patients had a median preoperative cell-free DNA level of 10,113 GE/mL, compared with patients with benign ovarian neoplasms (median, 2365 GE/mL; P < .0001) and controls (median, 1912 GE/mL, P < .0001). Cell-free DNA >22,000 GE/mL was significantly associated with decreased patient survival (P < .001). After adjusting for other clinical variables, preoperative cell-free DNA >22,000 GE/mL was an independent predictor (P = .02) for disease-specific survival. Analysis of the validation set confirmed significantly higher cell-free DNA levels in EOC (median, 13,672 GE/mL) and that cell-free DNA >22,000 GE/mL was associated with a 2.83-fold increased risk of death from disease (P < .001).

Conclusions: Preoperative plasma total cell-free DNA levels are significantly elevated in patients with EOC. Elevated plasma cell-free DNA is an independent predictor for death from disease in ovarian cancer.

Figure 1

Box plot of preoperative plasma CFDNA (GE/ml) for controls, patients with benign ovarian masses and ovarian carcinoma in the (A) Training Set (n=144) and (B) Validation Set (n=144). CFDNA level is significantly higher in the invasive carcinoma group when compared to women with benign ovarian tumors and controls with normal ovaries in both datasets.

Figure 2

Kaplan-Meier estimates of the probability of survival in patients with high CFDNA levels (≥ 22,000 GE/ml, dotted line) vs. those with low CFDNA levels (< 22,000 GE/ml, full line) in Training Set (A). This cutoff was validated in a separate cohort of patients, Validation Set (B). Two-sided log rank test provided a significant p-value < 0.001.

Figure 3

Receiver operating characteristic (ROC) curve of plasma cell-free DNA provides a sensitivity of 87% and a specificity of 87% to detect cancer, using a cut-off point of 4,500 GE/ml in the Training Set.