Circulating tumor DNA, liquid biopsy, and next generation sequencing: A comprehensive technical and clinical applications review

Circulating tumor DNA (ctDNA) represents a small fraction of the total circulating free DNA and its analysis is increasingly used for diagnostic, prognostic and treatment purposes of cancer. ctDNA is released into the bloodstream from tumor cells through different mechanisms including apoptosis, necrosis, autophagy, and necroptosis. Liquid biopsy is a method used to detect specific cancer mutations in ctDNA from the plasma fraction of a standard blood draw and has numerous applications. Adoption of this newly introduced method has many advantages for detecting mutations in blood where it is an alternative to the direct sampling of tissue through resection and biopsy, as the genetic mutations present in a patient may change following treatment, and conducting additional biopsies and resection may present risk to the health status of the patient since it is an invasive technique. In addition, the information acquired from a single biopsy of a tumor is limited and might fail to reflect its heterogeneity, leading to a false negative reading, and finally, an alternative to direct tissue sampling may also lessen the fiduciary and resource strain on caregivers and patients. Next Generation Sequencing (NGS) is gaining more presence in diagnostic molecular laboratories and is nowadays very close to embrace the field of liquid biopsies with an ultimate sensitivity and range of clinical applications. This review article is a first comprehensive technical overview of the ctDNA detection using NGS as a state-of-the-art technology.