结直肠癌的早期诊断在临床上迫切需要，然而，目前缺乏准确的非侵入性诊断方法。研究证实血浆DNA甲基化可以作为多种肿瘤早期辅助诊断的标志物，但血浆中的DNA含量很低，目前的DNA甲基化筛选工具难以解决血浆痕量DNA和筛选工具起始DNA含量要求较高的矛盾。且现有的甲基化检测方法难以针对血浆中的痕量DNA进行高灵敏度、高准确性、高重复性和绝对定量的检测。本项目基于临床需求，紧贴项目指南，针对结直肠癌早期诊断和血浆痕量DNA甲基化的检测现状，利用新型的850K甲基化芯片筛选血浆中潜在的敏感特异结直肠癌早期诊断甲基化标志物，建立痕量DNA甲基化位点的微液滴数字PCR检测方法，构建一种新型的血浆甲基化位点多参数联合辅助诊断指标。本项目从临床需求出发，通过检验医学、生物信息学和数学统计学多学科交叉研究，以期为结直肠癌的早期诊断提供一种非侵入性、敏感特异和准确性高的新型辅助诊断指标。

Early detection of colorectal cancer is urgently needed in clinical practices, however, there is currently a lack of accurate and noninvasive diagnostic methods. Studies have demonstrated that DNA methylation in plasma can serve as a biomarker for the early detection of kinds of cancer, but the content of DNA in plasma is low. The screening tool of DNA methylation is difficult to address the contradiction of trace DNA in plasma and the higher starting DNA content required by screening tools. And the methylation detection method is currently difficult for high sensitivity, high accuracy, high repeatability and absolute quantitative detection of the trace DNA in plasma. Based on clinical needs, kept with this project guide, aimed at the early detection of colorectal cancer and the detection of trace DNA methylation, the novel 850K methylation chip is used to screen potential, sensitive and specific methylation biomarker for the early detection of colorectal cancer in plasma, to establish the droplet digital PCR detection method of trace DNA methylation, and to build a novel multi-parameter diagnostic biomarker of methylation sites in plasma. Based on the clinical needs, by the combination of medical, bioinformatics and mathematical statistics multidisciplinary research, we aimed to provide a novel assistant diagnostic biomarker for noninvasive, sensitive specificity and high accuracy for the early detection of colorectal cancer.