Extracellular Nucleic Acids and Cancer

Abstract

Since the clear proof of the presence of tumor-associated genetic alterations in extracellular nucleic acids almost 20 years ago this field gained has attracted much interest. According to our current knowledge it seems as if all tumor-associated alterations found in tumor cells are also found in the extracellular environment. The isolation of extracellular nucleic acids from tumor patients and its genetic characterization with very sensitive and highly specific methods led to the concept of "liquid biopsy". This means that for follow-up analysis of tumor patients, the physicians no longer depend exclusively on a single examination of tissue biopsies (usually at the time of diagnosis) but are able by longitudinally analyzing the extracellular nucleic acids to follow the reaction of a tumor to e.g. a given therapy, the development of resistance mechanisms. In this chapter we will discuss the detection and characterization of different genetic (e.g. mutation analysis and structural variations as seen in microsatellites), epigenetic (e.g. hypermethylation of selected sequences) and regulatory alterations (as in different miRNA expression patterns found in tumor patients). We will also touch on some confounding factors that have to be taken into consideration as well as the functional and biological aspects of extracellular nucleic acids.