Evaluation of cell-free DNA as a biomarker for pancreatic malignancies

Background: Currently, no reliable blood-based assay for early detection of pancreatic ductal adenocarcinoma (PDAC) is available. Cell-free DNA (cfDNA) quantitation in patients' plasma has been recently applied in monitoring several cancer types. This study evaluates the diagnostic potential of cfDNA in PDAC patients. Methods: Plasma cfDNA levels and integrity ratio were assayed using quantitative real-time PCR of Alu-repeat amplicons in patients with pancreatic ductal adenocarcinoma (n=50), pancreatic neuroendocrine tumor (n=23), and chronic pancreatitis (n=20), as well as in healthy volunteers without evidence of pancreatic disease (n=23). Results: The total load of cfDNA, obtained by Alu83 quantitation, was the highest in PDAC patients than in any of the other patient groups (Welch t test; p<0.001) and was an average predictor of PDAC disease (AUC=0.664; CI, 0.56-0.77). A nonlinear association between Alu83 levels and subjects' age was detected (Spearman's rho=0.35; p<0.001) in the overall population, as well as within the PDAC patients' group (Spearman's rho=0.47; p<0.001). Necrosis-derived cfDNA fragments, quantitated with the Alu244 amplicon, were barely detectable in any of the samples and, in that respect, comparable between the different subject groups. CfDNA integrity estimation (Alu244/Alu83 ratio) was significantly affected by the limited detectability of plasma Alu244 levels. Conclusion: The lack of detectable levels of necrosis-derived cfDNA in pancreatic pathologies considerably affects the clinical use of such biomarker in PDAC patients. Different methods of analysis should be applied in the evaluation of the cfDNA diagnostic value in pancreas pathology.