Cell-free or circulating tumor DNA (ctDNA) is tumour DNA circulating freely in the blood of a cancer patient. Analysis of the fraction of mutant-alleles from ctDNA compared to normal-alleles from the patient’s normal genome provides opportunities for minimally-invasive cancer diagnosis, prognosis and tumor monitoring. ctDNA originates from dying tumor cells and can be present in a wide range of cancers but at varying levels and mutant allele fractions. The ctDNA is highly fragmented to around 170 bp and is cleared rapidly after surgery to remove tumors or chemotherapeutic treatment. Protocols to extract ctDNA generally aim to reduce contamination with normal DNA from leukocytes. This is achieved by rapid processing of whole blood by centrifugation to remove all cells, and analysis of the remaining plasma. The utility of circulating tumor DNA in cancer detection and monitoring has recently been shown via targeted sequencing of plasma.

In the present book, fifteen typical literatures about circulating tumor DNA published on international authoritative journals were selected to introduce the worldwide newest progress, which contains reviews or original researches on medical science, oncology, anatomical pathology, neoplasms biopsy, ect. We hope this book can demonstrate advances in circulating tumor DNA as well as give references to the researchers, students and other related people.