ABSTRACT

ABSTRACT MicroRNAs (miRNAs) comprise an abundant class of endogenous, small noncoding RNAs, 18-25 nucleotides in length that posttranscriptionally regulate gene expression through binding to target mRNAs. Ability of miRNAs to inhibit translation of oncogenes and tumor suppressor genes implies their involvement in carcinogenesis. In the last decade, the number of evidences that miRNAs might contribute to the regulation of apoptosis, cellular proliferation, and differentiation is constantly growing. Specic miRNA expression signatures have been identied in a variety of human cancers. Recently, miRNAs’ occurrence in the blood serum and plasma, where their levels are more stable, reproducible, and consistent among individuals of the same species, has been repeatedly observed. Circulating miRNAs have been successfully evaluated in various human cancers as promising novel noninvasive biomarkers of the early disease onset or its relapse. In this chapter, we describe the origin of circulating miRNAs, the principles of their immense stability, and proposed functions and comprehensively summarize studies focusing their signicance in breast, colorectal, lung, and prostate cancer, proposing their potential application in clinical routine as relevant biomarkers.