DNA fragments in the blood plasma of cancer patients: Quantitations and evidence for their origin from apoptotic and necrotic cells

Increased levels of DNA fragments have frequently been found in the blood p lasma of cancer patients. Published data suggest that only a fraction of th e DNA in blood plasma is derived from cancer cells. However, it is not know n how much of the circulating DNA is from cancer or from noncancer cells. B y quantitative methylation-specific PCR of the promoter region of the CDKN2 A tumor suppressor gene, we were able to quantify the fraction of plasma DN A derived from tumor cells, In the plasma samples of 30 unselected cancer p atients, we detected quantities of tumor DNA from only 3% to as much as 93% of total circulating DNA, We investigated possible origins of nontumor DNA in the plasma and demonstrate here a contribution of T-cell DNA in a few c ases only. To investigate the possibility that plasma DNA originates from a poptotic or necrotic cells, we performed studies with apoptotic (staurospor ine) and necrotic (staurosporine plus oligomycin) cells in vitro and with m ice after induction of apoptotic (anti-CD95) or necrotic (acetaminophen) li ver injury. Increasing amounts of DNA were found to be released in the supe rnatants of cells and in the blood plasma samples of treated animals, A cle ar discrimination of apoptotic and necrotic plasma DNA was possible by gel electrophoresis. The same characteristic patterns of DNA fragments could be identified in plasma derived from different cancer patients. The data are consistent with the possibility that apoptotic and necrotic cells are a maj or source for plasma DNA in cancer patients.