Circulating MicroRNAs as Cancer Biomarkers: Can They Play a Role in Clinical Practice? Short Review

microRNAs (miRNAs) are a large family of short noncoding RNA sequences which modulate gene expression and regulate a wide range of biological processes. There is evidence that miRNAs may have a role in molecular mechanisms linked to tumorigenesis and a lot of studies have proven that some miRNAs are closely correlated with cancer. miRNAs are not only contained in tissue cells but they are also detectable in extracellular sites, as plasma, urine, cerebrospinal and other body fl uids where they are remarkably stable, so that may be identifi ed and measured. Since tumors alter the normal concentrations of circulating miRNAs, these oligo nucleotides can be used as cancer biomarkers. Circulating miRNAs detection may be used for early diagnosis, staging, follow up, assessment of therapeutic responses and therapy outcomes in several types of human cancer as colorectal cancer, pancreatic adenocarcinoma, lung cancer and malignant pleural mesothelioma, urinary and prostate cancer, breast cancer, hematologic malignancies, glioblastoma and others. Quantitative real-time Polimerase Chain Reaction (qRT-PCR) is one of the most sensitive techniques for quantifying circulating miRNAs. Deep sequencing technology has recently emerged as an attractive approach for miRNA analysis; in some cases this technique showed more specifi city and sensitivity compared to qRT-PCR and Microarray, also allowing identifi cation of novel MiRNA isoforms. Given that current serological cancer biomarkers, commonly employed in follow up, have low specifi city and sensi tivity, it is plausible that circulating miRNA detection can be included in future routine clinical examinations for management of cancer patients, although costs and wide availability of quantifying techniques could represent a critic limit. Further comparative studies will be required. Mini Review Circulating MicroRNAs as Cancer Biomarkers: Can They Play a Role in Clinical Practice? Short Review Angelo Michele Carella*, Teresa Marinelli, Armando Melfi tano, Michele Di Pumpo, Giovanni Modola, Matteo Conte and Angelo Benvenuto Internal Medicine Department, T Masselli-Mascia Hospital, San Severo (Foggia), Italy Dates: Received: 02 December, 2016; Accepted: 16 December, 2016; Published: 17 December, 2016 *Corresponding author: Angelo Michele Carella, Internal Medicine Department, T Masselli-Mascia Hospital, San Severo (Foggia), Italy, E-mail:

Introduction microRNAs (miRNAs) are a large family of short noncoding RNA sequences [1] which modulate gene expression and regulate a wide range of biological cell processes [2].
There is evidence that miRNAs may have a role in molecular mechanisms linked to cellular pathways of certain diseases, as viral infections, diabetes and cardiovascular disease; moreover, miRNA have been shown to regulate several processes involved in tumorigenesis [2][3][4][5].
miRNAs are not only contained in tissue cells but they are also detectable in extracellular sites, as plasma, urine, cerebrospinal and other body fl uids; miRNAs are carried in body fl uids within small membrane vesicles (exosomes), in the form of high-density lipoprotein complexes, or complexed to carrier proteins (argonaute-2 proteins). Extracellular microRNAs in exosomes may be transferred to other cells, altering gene expression and changing the functional effects of receivers [6][7][8].
The presence of endogenous miRNAs in microparti-cles makes circulating miRNAs remarkably stable in the bloodstream even under conditions as harsh as boiling, low or high pH, long-time storage at room temperature, and multiple freeze-thaw cycles, so that they may be identifi ed and measured in the circulation and can be used as potential disease biomarkers [5].
A lot of studies have proven that expression of some miRNAs is closely correlated with cancer development and altered levels of miRNA have been related to the maintenance of cancer stem cells, neoangiogenesis, metastasis and epithelial-mesenchymal transition, which contribute to the malignancy [9-11]. It has also been shown that microRNAs may be responsible for other biological processes, such as cancer-associated infl ammation and tumor drug resistance [12].

Aim of the Research
The purpose of the present review was to examine the latest evidences on circulating miRNAs as cancer biomarkers and evaluate whether the detection of these nucleotides can play a role in daily clinical practice.

Material and Methods
A review of recent literature has been carried out via Pub Med database, using these search term: microRNA, cancer biomarkers, clinical practice. Search was not limited by language or human subjects. All the found items, published in the last fi ve years were analysed. Additional articles were selected from the bibliographies of the quoted references.

Results
91 items were obtained: 55 reviews (9 systematic reviews), The analysis of obtained data showed that a lot of miRNA is associated with cancer and many types of miRNA have been identifi ed in several types of human cancer, as summarized in Table 1.
There is wide evidence that tumors alter the normal concentrations of miRNAs in biological fl uid, thus these oligonucleotides may serve as cancer biomarkers. These fi ndings will be discussed in this brief review with related references.
In cancer management, circulating miRNAs detection may be used for early diagnosis, cancer staging, prognosis and patient follow up to individuate early relapses; moreover, there are promising data to extend this assay for predicting specifi c therapeutic responses and also to assess therapy outcomes (Table 1). Since miRNAs are also detectable in extracellular sites, as plasma and other body fl uids where they may be measured and since tumors alter the normal concentrations of circulating miRNAs, these oligo nucleotides can be used as biomarkers for cancer detection [14].

Discussion
The study of miRNA has thus become a rapidly emerging fi eld in oncology and the detection of miRNA expression is a very important fi rst step in miRNA exploration.
Several techniques are available for quantifying circulating miRNAs, such as quantitative real-time Polimerase Chain Reaction (qRT-PCR) [15], Northern blotting [16], bead-based fl ow Cytometry [17], Microarray [18] or Deep sequencing [19]. However, of these assay, qRT-PCR seems superior because of its high sensitivity, specifi city and reproducibility; moreover qRT-PCR requires less amount of RNA sample, usually more than 1 μg, but the number of miRNAs possible to analyze and RNA quantity may represent limitations for this assay [15].
Conversely, Deep sequencing technology has recently emerged as an attractive approach for miRNA analysis; in some cases this technique showed most specifi city and sensitivity compared to qRT-PCR and Microarray, also allowing identifi cation of novel miRNA isoforms [20]. Actually, it is well known that a single gene may, in turn, be regulated by multiple miRNAs, therefore, given the large number of miRNAs annotated in the human genome, 30%-80% of human genes are predicted to be infl uenced by miRNAs. Moreover, a single miRNA infl uences the expression of hundreds of unique miRNAs and aberrant miRNA expression may affect a multitude of transcripts and profoundly infl uence cancer-related signaling pathways. This situation generates a complex net work, and the analysis of miRNA panels is con sequently more effi cient in cancer studies than the analysis of a single miRNA [21].
Thanks to these analysis methods and techniques that allow measurement of multiple miRNA types, these circulating nucleotides may be used for early diagnosis, staging, follow up, assessment of therapeutic responses and therapy outcomes in several types of human cancer as colorectal cancer, pancreatic adenocarcinoma, bladder cancer, lung cancer and malignant pleural mesothelioma, urinary and prostate cancer, breast cancer, hematologic malignancies, glioblastoma and others [22]. The current methods used for miRNAs detection usually requires high costs and this aspect could limit their use in daily clinical practice. However, in this way, research should try to overcome this limiting aspect, although spending review in health care and cost-containment measures could represent a critical ethical problem in a delicate fi eld as oncolgy [27].
In our research we have not found comparative studies, in terms of specifi city, sensibility and costs, between miRNAs and other conventional cancer biomarkers commonly used in clinical practice. It is desirable that, in future, comparative studies will be undertaken.