Extracellular nucleic acids and their potential as diagnostic, prognostic and predictive biomarkers.

Extracellular nucleic acids (NAs), both DNA and mRNA, have been found to exist in many biological media, including serum, plasma, saliva, urine, semen, milk and bronchial lavage, as well as cell culture supernatants. Analysis of such NAs as potential diagnostic, prognostic or predictive biomarkers for cancer has indicated that, while these NAs are detected in both plasma and serum from both healthy individuals as well as those suffering from a broad range of cancer types, their overall concentrations in the circulation are generally higher in cancer than in normal conditions. Indeed, the detection of specific mRNAs (by RT-PCR/qPCR and, more recently, by microarrays) has been associated with the presence of cancer, supporting their potential as useful biomarkers. Furthermore, it has been proposed that these extracellular mRNAs are not inert, but may have functional relevance. Evidence suggests that such extracellular NAs also have potential as biomarkers for a range of other pathological conditions and in forensic science. In conclusion, it seems that the field of extracellular NAs has great potential to be exploited by the development of minimally-invasive diagnostic, prognostic and predictive assays for cancer if it is ensured that relevant and adequate controls are included in all studies.