microRNA expression profiles as decision-making biomarkers in the management of bladder cancer

Bladder cancer (BC) is generally divided into non-muscle-invasive BC (NMIBC) and muscle-invasive BC (MIBC). The standard treatment protocol for MIBC patients is radical cystectomy preceded by neoadjuvant chemotherapy (NAC). About one-half of the MIBC patients show a priori resistance to chemotherapy, and are therefore exposed to the risks of disease progression and toxicity from ineffective NAC. The discovery of microRNA (miRNA) regulation in tumorigenesis has provided new directions for the development of a new type of BC biomarkers. In this review, we describe the emerging miRNAs as BC biomarkers for different purposes, including diagnosis, prognosis and therapeutic response. miRNA expression profile changes with alteration of the tissue phenotype. This phenomenon is utilized to predict tumor diagnosis, cancer subclass, disease stage, prognosis and therapeutic response. We classified the miRNAs which are involved in bladder cancer according to malignant potential, chemoresistance, discrimination between normal to cancerous and clinical outcome. Focusing on the major obstacle regarding MIBC patient's NAC response, we summarized the miRNAs that are deregulated and have the potential to identify the patients resistant to NAC, such as miR-34, miR-100, miR-146b and miR-9 and miR-193a-3p. In conclusion, miRNAs expression profile of bladder cancer patient is a promising tool that can serve as biomarker for different aims. Based on this profile we propose upfront radical cystectomy instead of standard NAC to those MIBC patients who are at higher risk for chemoresistance and poor response.