中文摘要：

循环核酸（circulating nucleic acid,CNA）是指存在于血液（血清或血浆）等体液中的细胞外游离DNA和RNA,与生理和病理状态下的细胞代谢密切相关,循环DNA和RNA水平的检测及其在基因诊断等方面的应用对于恶性肿瘤等疾病的诊断和监测具有十分重要的意义。近期人们在进行循环DNA、RNA分子检测的同时,在循环微小RNA（microRNA,miRNA）方面也做了许多的工作,研究结果使得与肿瘤相关的核酸分子检测这一领域变的更加让人振奋。在血液中检出肿瘤特异性的miRNA并将其作为肿瘤的生物学标志对于早期诊断肿瘤具有至关重要的意义。

英文摘要：

Circulating nucleic acids （CNAs） are extracellular nucleic acids found in cell-free serum, plasma and other body fluids from healthy subjects as well as in patients. The ability to detect and quantitate specific DNA and RNA sequences has opened up the possibility of diagnosis and monitoring of diseases, especially in the field of cancer. Furthermore, in some recent studies it has been suggested a kind of non-coding RNA-microRNA （miRNA） , also exist in cell-free serum and plasma, highlighting the field of using CNAs to diagnose cancer. As a novel tumor marker, tumor-specific circulating miRNAs holds great promise in early diagnosis of cancer.