Circulating Nucleic Acids as Potential Biomarkers of Cancer
Both DNA and miRNA (see later in this chapter) have been studied as cancer biomarkers. Circulating cell-free DNA (ccf-DNA) levels have been studied in plasma and serum samples as biomarkers of cancer. An elevated level of ccf-DNA has been detected in the circulation of cancer patients in comparison with healthy controls (Kohler et al. 2011). Since ccf-DNA in cancer patients often bears similar genetic and epigenetic features to the related tumor DNA, there is evidence that some of the ccf-DNA originates from tumor tissue. This, and the fact that ccf-DNA can easily be isolated from the circulation and other body fluids of patients, makes it a promising candidate as a noninvasive biomarker of cancer. ccf-DNA may also represent an important source of biomarkers at several steps of carcinogenesis, including early detection of preneoplastic lesions and monitoring of cancer. Moreover, levels of plasma DNA could be tested as a potential intermediate biomarker of the efficacy of intervention. It is possible to develop a simple cost-effective blood test, with high sensitivity and specificity that has potential for screening high-risk individuals, for prognostic purposes and to be used as intermediate end-points of efficacy in chemo- prevention and therapeutic trials (Catarino et al. 2012).