DNA Hypomethylation in Pancreatic Cancer Tissues Before Treatment, Defined by KRAS-mutated Circulating Tumor DNA, is Associated With Poor Prognosis

Objects: Aberrant hypomethylation of long interspersed nucleotide element-1 (LINE-1) and satellite alpha (SATa) in pancreatic cancer cells increases malignant potential. In addition, circulating tumor DNA (ctDNA) is likely to be associated with micrometastasis and appears more frequently in advanced pancreatic ductal adenocarcinoma (PDAC) patients. In this study, we elucidated the relationship between these factors. Methods: A total of 37 patients with PDAC who underwent surgery or first-line chemotherapy were selected in 2014-2017. DNA extracted from surgical, or biopsy specimens was used to calculate the relative demethylation levels (RDLs) of the LINE-1 and SATa using methylation-specific quantitative PCR. KRAS -mutated ctDNA was monitored using droplet digital PCR. Receiver operating characteristic curve analysis was performed to determine the cut-off values of LINE-1 and SATa RDLs before and after surgery or during first-line chemotherapy based on ctDNA status (presence or absence). Results: Median LINE-1 RDL before treatment were higher in patients with ctDNA than in those without but these cutoff values (LINE-1≥0.058 and 0.055) peri-treatments did not link to prognosis ( P =0.762 and 0.933). Conversely, the cutoff value of SATa RDL (SATa ≥0.150) based on ctDNA status after treatments showed significant association with poor prognosis ( P =0.038). On the other hand, the cutoff value of SATa RDL (SATa ≥0.155) before treatment was found to have no association with prognosis ( P =0.408). Conclusions: Evaluating pre-treatment tumor DNA hypomethylation together with KRAS -mutated ctDNA status after surgery or initiation of first-line chemotherapy is associated with poor prognosis in PDAC.