[Circulating Tumor DNA (ctDNA) Detection Using BEAMing and Its Clinical Significance.].

In cancer, companion diagnostics accompanied by molecular-targeted drugs have been developed and launched over the last decade, leading to marked improvements of patients' treatments and outcomes. Alt- hough most of them are tested using tissue samples, sometimes it is difficult to obtain a biopsy for some types of cancers because of the patient's risk and performance status. Recently, extensive clinical research regarding "Liquid Biopsy", such as circulating tumor DNA (ctDNA), has been performed. It is considered that "Liquid Biopsy" has the potential to overcome the issue of tissue-based molecular diagnostics. "BEAMing" is one of the digital PCR methods invented by Prof. Bert Vogelstein's group from Johns Hop- kins University. This technology enables highly sensitive detection, at 0.01% of ctDNA in plasma, which outperforms general PCR methods. Regarding BEAMing, extensive research on the clinical significance of ctDNA detection has been done, especially in three fields: response prediction, response/recurrence monitoring, and molecular-targeted drug resistance monitoring. In this article, I will discuss the possibility of BEAMing and ctDNA testing as future diagnostics.