Non-coding RNAs as biomarkers in liquid biopsies with a special emphasis on extracellular vesicles in urological malignancies

Introduction: Non-coding RNAs (ncRNAs) are important regulators of cellular signaling in tumor-related processes. They can not only be detected in tumor tissues, but also in body fluids. ncRNAs are released into circulation as cell-free RNAs in at least two ways: bound to proteins like Ago2 or packed in extracellular vesicles (EV). Therefore, they have a great potential to serve as biomarkers in liquid biopsies. This review gives an overview of the current knowledge concerning ncRNAs and EVs as putative liquid biomarkers in urological tumor diseases.Areas covered: Literature was searched for ncRNAs including microRNA, long non-coding RNA, small interfering RNA, small nuclear RNA, small nucleolar RNA and PIWI-interacting RNA in blood (serum, plasma) and urine samples from urological tumor (urothelial, kidney, prostate, testicular germ cell, penile cancer) patients.Expert opinion: The data demonstrate an important potential of circulating non-coding RNAs as biomarkers in liquid biopsies for diagnosis and follow-up of patients with urological tumors. To translate these markers into clinical practice, independent and prospective validation, standardization of isolation and quantification techniques are inevitable. Another task is the development of predictive ncRNA biomarkers to overcome problems associated with tumor heterogeneity and to select patients individually for systemic therapies.