Figure 1.

Secretion of cfDNA from tumor cells. Cell death by apoptosis, pyroptosis, or necrosis is one of the most important sources of ctDNA in body fluids; however, even without cell death, cfDNA/ctDNA has been found in the medium. This means that live cells can actively release cfDNA. Due to autophagy and exosome activity, the active secretion of cfDNA through microvesicles has also been observed. Once the cfDNA is released into the body fluids, it is detected by various methods, based on its size, concentration, frequency of repeats, or presence of mutations.