循环核酸是指存在于血浆或血清等体液中的细胞外游离状态的核酸。早在1948年,Mandel与Métais[1]首次发现了人类血液中循环核酸的存在,但当时并未引起学术界太大的关注。直到1994年,肿瘤患者血液中RAS基因片段的检测及应用[2],医学界才重新认识到循环核酸的重要性。鉴于循环核酸在肿瘤无 Cyclic nucleic acids refer to nucleic acids that exist in extracellular free state in body fluids such as plasma and serum. As early as 1948, Mandel and Métais [1] first discovered the existence of circulating nucleic acids in human blood, but at that time did not cause much academic attention. Until 1994, cancer patients with RAS gene in the blood of the detection and application of fragments [2], the medical community to re-recognize the importance of circulating nucleic acid. Given the absence of circulating nucleic acids in the tumor