LAUSR

Despite the remarkable diagnostic and therapeutic advances in recent years, cancer continues to rank as the second leading cause of global deaths, accounting for 9.6 million deaths in 2018 (1). One of the reasons cancer is fatal is that it is a disease of the genome. Abnormal changes to certain genes of cells cause cell replication malfunction and death, thus leading to the proliferation of deadly cancer cells and their distribution throughout the body in an uncontrolled manner. The nature of cancer as a genetic disease has challenged many researchers to investigate the association of mutated cancer DNA with the stage, type, and patient's family history of cancers. In particular, tumor-derived fragmented cancer DNA in the bloodstream, which is known as circulating tumor DNA (ctDNA), has recently garnered attention because of its considerable potential as a cancer biomarker for the diagnosis of specific cancers. Currently, the detection of ctDNA from blood samples is performed via liquid biopsy, in contrast to the conventional tissue biopsy, and is one of the hottest topics in cancer diagnostics. Considering the drawbacks of tissue biopsy, which is currently the only definitive clinical way to diagnose most cancers, much simpler blood tests would be highly attractive to both patients and medical doctors. However, owing to technical challenges, the investigation of ctDNA has been limited to research laboratories, and ctDNA has not yet been used for the clinical diagnosis of cancer in patients (2). In addition to the genetic changes associated with cancers revealed by biomarkers such as ctDNA, abnormal epigenetic alterations have been investigated intensively as an important aspect of cancer cells. In particular, DNA methylation is of utmost interest because it is frequently observed at a high occurrence rate in most types of cancer cells, demonstrating its strong potential as a universal cancer biomarker. …