ctDNA, also known as circulating tumor cell DNA, refers to the DNA fragment that may exist in the blood from a small number of necrotic secreted tumor cells, which can be detected by a highly sensitive test method, and can be used for the early diagnosis of some cancers, as well as the follow-up evaluation of treatment effects after tumor treatment. Of course, this index must be done under qualified testing institutions, and generally not all hospitals and biological companies can do it. In combination with this index, there are other imaging tests and endoscopy, which are of high value for early cancer diagnosis, but one cannot diagnose the presence of cancer by ctDNA test alone.