Research Of Circulating Cell-free DNA In Serum Of Colorectal Cancer Patients:Detection And Application In The Clinic

BackgroundColorectal cancer (CRC) is one of the most common cancers in the world. With the change of living habits and diet structure and the acceleration of the aging process of population, the incidence of colorectal cancer in China shows an upward trend in recent years. Early diagnosis of colorectal cancer is very important for detecting, treating and improving the prognosis of patients in time. However, there are still many difficulties in the early diagnosis of colorectal cancer. Serum tumor marker detection is one of the most common methods for early detection of coloorectal cancer, but its sensitivity and specificity are not so ideal. In recent years, peripheral blood cf-DNA plays an important role in early diagnosis of colorectal cancer as a new tumor marker. In this study, cf-DNA is extracted from peripheral blood of patients along with tumor tissue DNA for cf-DNA concentration detection, exome sequencing and bioinformatics analysis, trying to find out the related loci for early diagnosi of colorectal cancer. The expression of PTEN and NOK in coclrectal carcinoma and adjacent normal tissue is studied by immunohistochemical staining, in order to find out whether there is a correlation between the expression of PTEN/NOK and the differentiation degree of tumor.Methods1. This study recruits patients with ulcerative colitis (UC), colorectal adenoma, early cancer and advanced cancer visiting PUMC from 2015.9 to 2016.5, collecting primary tumor speciments and adjacent normal tissues by colonoscopy or surgery along with peripheral blood. Tumor speciments and adjacent normal tissues were collected in pairs in the same patient. DNA were extracted from each speciment and the purified, fragmented, amplificated and captured for cf-DNA concentration detection and exome sequencing.2. This study recruits patients with colorectal cancer received surgery in PUMC from 2015.1-2016.6,taking normal colonic mucosa above 8cm from adjacent cancer edge without hyperplasia for self control. The hostological diagnosis was confirmed by immunohistochemical staining after HE staining.Results1. This study recruits 19 samples from 6 patients with ulcerative colitis (UC), colorectal adenoma, early cancer and advanced cancer. Through the peripheral cf-DNA concentration detection, we find out that cf-DNA concentration of UC and cancer patients are higher than those of adenoma patients.2. The expression of PTEN in normal colonic mucosa is higher than that in colon carcinoma, and the expression of NOK in tumor tissue is higher than in normal colonic mucosa. The distribution of NOK in middle and high differentiated tumor tissue is close to cell membranes.ConclusionsPeripheral cf-DNA concentration detection combined with NGS can be used in the early diagnosis of colorectal cancer, but it needs to expand the sample size and further experimental research before widely used in clinic. Deletion and mutation of PTEN may be related to the occurrence of colorectal cancer. NOK may be related to the occurrence and development of colorectal cancer. The molecular mechanism of PTEN and NOK, along with the clinical application prospects deserve further research.