The Ratio of ssDNA to dsDNA in Circulating Cell-Free DNA Extract is a Stable Indicator for Diagnosis of Gastric Cancer.

Due to the different mechanisms of cell-free DNA production, the single-stranded DNA to double-stranded DNA ratio in blood maybe different between healthy individuals and gastric cancer (GC) patients. We aimed to explore the potential application of this ratio in GC diagnosis. The plasma cell-free DNA extracts from 118 healthy individuals and 106 GC patients were prepared. The levels of single-stranded DNA or double-stranded DNA in plasma, and the single-stranded DNA to double-stranded DNA ratio on the diagnostic efficiency for GC were assessed with ROC curve. The relationships between this ratio and the clinical characteristics of GC patients were analyzed. The ratios in 63 GC patients before and after surgery were compared. In healthy individuals, the single-stranded DNA to double-stranded DNA ratio was not affected by factors including age, gender and BMI, and subjected to normal distribution (P = 0.1090). GC patients had a lower value of this ratio than healthy individuals (P < 0.0001). Considering this ratio as a GC diagnostic indicator, the area under ROC curve (AUC) was 0.923[95% confidence interval (CI):0.880-0.955]. This ratio in unresectable GC was obviously lower than that in resectable GC (P = 0.0045). There was a rank correlation between this ratio and GC TNM staging (rho = -0.266, P = 0.0058), but it had no correlation with tumor size (r = 0.14, P = 0.145). Additionally, this ratio was not affected by hemolysis and repeated freeze-thaw of blood samples, and was significantly elevated after surgery(P < 0.0001). The single-stranded DNA to double-stranded DNA ratio in plasma is a stable non-invasive indicator for GC diagnosis.