cfDNA (cell-free DNA) represents small pieces of DNA floating outside of the cells in various body fluids including blood. In healthy individuals, cfDNA exists in the bloodstream at concentrations ranging from 1 to 10 ng/ml. It plays a role in various physiological and pathological processes, including immunity, blood clotting, aging, and cancer.
In the case of cancer patients, a portion of cfDNA originates from tumors. This tumor-derived DNA is referred to as ctDNA (circulating tumor DNA), and it carries the same genetic mutations found in the primary tumor cells. Typically, ctDNA is released when tumor cells die and can be derived from both circulating tumor cells and viable tumor cells.