Abstract
The last two decades of cancer research have been devoted in two directions: (1) understanding the mechanism of carcinogenesis for an effective treatment, and (2) improving cancer prevention and screening for early detection of the disease. This last aspect has been developed, especially for certain types of cancers, thanks also to the introduction of new concepts such as liquid biopsies and precision medicine. In this context, there is a growing interest in the application of alternative and noninvasive methodologies to search for cancer biomarkers. The new frontiers of the research lead to a search for RNA molecules circulating in body fluids. Searching for biomarkers in extracellular body fluids represents a better option for patients because they are easier to access, less painful, and potentially more economical. Moreover, the possibility for these types of samples to be taken repeatedly, allows a better monitoring of the disease progression or treatment efficacy for a better intervention and dynamic treatment of the patient, which is the fundamental basis of personalized medicine. RNA molecules, freely circulating in body fluids or packed in microvesicles, have all the characteristics of the ideal biomarkers owing to their high stability under storage and handling conditions and being able to be sampled several times for monitoring. Moreover, as demonstrated for many cancers, their plasma/serum levels mirror those in the primary tumor. There are a large variety of RNA species noncoding for proteins that could be used as cancer biomarkers in liquid biopsies. Among them, the most studied are microRNAs, but recently the attention of the researcher has been also directed towards Piwi-interacting RNAs, circular RNAs, and other small noncoding RNAs. Another class of RNA species, the long noncoding RNAs, is larger than microRNAs and represents a very versatile and promising group of molecules which, apart from their use as biomarkers, have also a possible therapeutic role. In this review, we will give an overview of the most common noncoding RNA species detectable in extracellular fluids and will provide an update concerning the situation of the research on these molecules as cancer biomarkers.
Highlights
In oncology, a biomarker is defined as a measurable alteration in a sample that is associated with cancer condition or that could have a predictive or prognostic value
Predictive biomarkers are useful for screening and for a better diagnosis, but mostly they could serve as a starting point to understand the biological pathways and regulatory mechanisms involved in the pathology and could serve as a potential target for drugs [2]
Liquid biopsies can be used in the early detection of cancer, before radiologic and imaging events have detected the presence of a tumor
Summary
A biomarker is defined as a measurable alteration in a sample that is associated with cancer condition or that could have a predictive or prognostic value. MiR-21-5p was a good biomarker in tissues and body fluids for leukemia, lymphoma, pancreatic, gastric, esophageal, colorectal, renal, breast, prostate, and ovarian cancers, and for non-small-cell lung cancer (NSCLC) and glioma. The number of studies covering miRNAs implicated in all cancers and detectable as biomarkers in body fluids is extremely high, considering the increase of interest of researchers on these molecules in the last years. Vychytilova-Faltejskova et al concluded that piRNAs could serve as promising noninvasive biomarkers for early detection of colon cancer [159]
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