Secretory miRNAs as novel cancer biomarkers

MicroRNAs (miRNAs) are a class of small non-coding RNAs that degrade or block target mRNAs at the post-transcriptional level. Many studies have shown that miRNA dysregulation is involved in cancer initiation, invasion, metastasis, and so forth. Notably, recent studies have revealed secretory miRNA levels in blood and other body fluids to correlate significantly with cancer progression, therapeutic response and patient survival. Thus, secretory miRNAs have demonstrated great potential as powerful and non-invasive cancer biomarkers. Herein, we summarize the current progress of secretory miRNAs in different cancer types and analyze the potential mechanisms of miRNA secretion. Then, we discuss the different approaches to miRNA detection in body fluids and the advantages of secretory miRNAs as biomarkers for early cancer diagnosis and the prediction of therapeutic efficacy. Finally, we list the current progress of secretory miRNAs as cancer biomarkers in clinical trials. Although several issues remain to be clarified, such as the mechanisms of miRNA secretion, it is only a matter of time before miRNAs are widely utilized as cancer biomarkers.