[Clinical Significance of Circulating Tumor DNA and Its Future Prospects].

"Liquid biopsy"is a diagnostic medium to detect very small amount of tumor-derived molecules in blood for selecting precise clinical treatments and giving a diagnosis. This article focuses on circulating tumor DNA(ctDNA)and describes its features, clinical significance as well as future prospects with recent findings in this field. "Liquid biopsy"using ctDNAis facilitated by recent developments of highly sensitive technologies, including digital PCR. "BEAMing"is a digital PCR method that can detect rare mutations in ctDNAand will be introduced with some clinical evidences in this article. ctDNAis tumorderived fragmented DNAthat is circulating freely in the blood of a cancer patient. Tests for ctDNAare less invasive, easier than tissue-based tests to collect specimens and can be used repeatedly regardless of any cancer types. Emerging clinical evidences indicate that ctDNAtests show a high concordance rate with tissue-based tests in the identification of oncogene genotypes and can be used for real-time monitoring in vivo, such as prediction of clinical treatments, recurrence and drug resistance. "Liquid biopsy" using ctDNAcontinues to develop, but is promising to complement conventional tissue-based tests. Clinical applications of ctDNAtests are expected to expand as a useful diagnostic tools in areas of therapy selection and monitoring for drug resistance.