RESUMO
Small amounts of DNA circulate in both healthy and diseased human plasma/serum, and increased concentrations of DNA are present in the plasma of cancer patients. Characteristics of tumor DNA have been found in genetic material extracted from the plasma of cancer patients. These features include decreased strand stability, the presence of specific oncogene or tumor suppressor gene mutations, microsatellite alterations, Ig rearrangements and hypermethylation of several genes. The results obtained in many different cancers have opened a new research area indicating that plasma DNA might eventually be a suitable target for the development of noninvasive diagnostic, prognostic and follow-up tests for cancer. Following the discovery of tumor derived DNA in plasma or serum, cell-free fetal DNA has also been found in maternal plasma and serum. This discovery provides an easily accessible source of fetal genetic material for prenatal diagnosis.