Chasing the Role of miRNAs in RCC: From Free-Circulating to Extracellular-Vesicle-Derived Biomarkers

Simple Summary Renal cell carcinoma (RCC) is the most common type of kidney cancer. The therapeutic strategies are based on surgery and/or specific therapies able to inhibit growth factors that have been shown to promote the growth and spread of tumors. Currently, there is no established biomarker which helps in early diagnosis and in better disease monitoring with a high sensitivity. Much information could be provided by body fluids, especially blood liquid biopsy (LB), that are increasingly interesting to researchers. LB is a non- or minimally invasive procedure that could allow clinicians to monitor cancer evolution, also thanks to the presence of small vesicles known as extracellular vesicles (EVs) secreted by tumor cells and containing useful information. In particular, growing interest is focused on small RNA molecules (miRNAs) that are involved in tumor growth and could represent potential diagnostic, prognostic, and predictive biomarkers in RCC, as we summarize in this review. Renal cell carcinoma (RCC) is the second most common cancer of the urinary system. The current therapeutic strategies are based on partial or total nephrectomy and/or targeted therapies based on immune checkpoint inhibitors to which patients are often refractory. Preventive and screening strategies do not exist and the few available biomarkers for RCC are characterized by a lack of sensitivity, outlining the need for novel noninvasive and sensitive biomarkers for early diagnosis and better disease monitoring. Blood liquid biopsy (LB) is a non- or minimally invasive procedure for a more representative view of tumor heterogeneity than a tissue biopsy, potentially allowing the real-time monitoring of cancer evolution. Growing interest is focused on the extracellular vesicles (EVs) secreted by either healthy or tumoral cells and recovered in a variety of biological matrices, blood included. EVs are involved in cell-to-cell crosstalk transferring their mRNAs, microRNAs (miRNAs), and protein content. In particular, transferred miRNAs may regulate tumorigenesis and proliferation also impacting resistance to apoptosis, thus representing potential useful biomarkers. Here, we present the latest efforts in the identification of circulating miRNAs in blood samples, focusing on the potential use of EV-derived miRNAs as RCC diagnostic and prognostic markers.