Once miRNAs are released from these structures into the bile, they are likely rapidly degraded. There is a real need for innovative tools to accurately diagnose BTC. Currently, the presence of carcinoembryonic antigen and carbohydrate 19-9 in serum serve as a standard for the clinical diagnosis of BTC. As shown in Table 1, however, the sensitivity of this test is not as high as that achieved by our miRNA analysis. In eight of nine BTC cases, serum CEA levels did not increase, even though cancer was present. Additionally, serum CA-19-9 levels were only increased in certain patients, probably because of cholestasis. Diagnostic imagining techniques such as endoscopic ultrasonography and intraductal ultrasonography are used when BTC is suspected. EUS allows for a good view of the distal extrahepatic biliary tree, gall bladder, regional lymph nodes and vasculature. Ro¨ sch et al. compared the diagnostic accuracy of endoscopic retrograde cholangiopancreatography, MRCP, CT, and EUS in 50 patients with biliary strictures. Moreover, in a recent meta-analysis, EUS had a sensitivity of 78% and a specificity of 84%. Intraductal ultrasonography with wireguided, thin-caliber, high-frequency probes is performed during ERCP, and in previous studies showed accuracy rates for distinguishing benign and malignant strictures of 76–90%. In addition to imaging techniques, histological methods such as bile cytology, brush cytology, and forceps biopsy are mandatory for definitive diagnosis. Bile cytology and brush cytology have only modest accuracy rates for determining malignancy, ranging from 30 to 70% in most published studies. Forceps biopsy, which has a higher accuracy rate than the other histological tests, is not widely used because it requires a specialized device and technique. Similarly, the more specialized EUS-guided fine-needle aspiration biopsy, with a diagnostic sensitivity of 43 to 86% for biliary strictures, is currently only used for pancreatic tumors and inferior bile duct strictures and has not been approved for use in other conditions. The low diagnostic accuracy of some of the currently used tests confirms that BTC can be difficult to diagnose. In view of the poor prognosis for BTC, it is desirable to improve the ease and accuracy of testing. The results of our investigation indicate that measuring bile miRNAs can improve the speed and accuracy of diagnosing BTC. Furthermore, bile analysis is feasible because bile miRNAs are stable and can be easily extracted and analyzed in clinical settings.