Liquid biopsy involves testing extracellular DNA (cfDNA – circulating, cell-free DNA) circulating in the blood and deriving from normal or cancer cells. Analysis of a small amount of blood can be a rich source of information about the health status of cancer patient. Liquid biopsy may be an alternative to tumor biopsy, but it presents particular value in cases of inaccessibility of tissue samples and the possibility of repeating it many times. The tumor-derived cfDNA fraction is called circulating tumor DNA (ctDNA) in oncology. An example of ctDNA may be the genome sequences of the