405 Background: MicroRNAs (miRNAs), a class of small RNAs, have been intensely investigated recently because of their important regulatory role in gene expression. Circulating miARNs are potential biomarkers for cancer not only abundant in blood, but also very stable, which are important prerequisites as clinical biomarkers. Detection of circulating tumor cells (CTC) may provide diagnostic and prognostic information in genitourinary renal tumors. The aim of this work is identify miRNAs potentially useful for CTC detection in blood samples from patients with renal tumors to assess their potential clinical significance. Methods: We examined blood levels of three miRNAs, let-7c, miR-200c and miR-31 in 48 patients with renal tumors with locally advanced or metastatic disease and 18 healthy persons using quantitative real-time PCR. The clinicopathologic characteristics of the population under consideration include among other: sex, age, tumor location, histological type, Fuhrman grade, tumor size, number of involved nodes, tumor stage, time to progression and overall survival. Results: We found that the median levels of miRNAs, let-7c, miR-200c and miR-31 were significantly higher in patients with renal tumors than those in healthy controls (p=.002, p=.000 and p=.004, respectively). Receiver-operator characteristic (ROC) curve analyses indicate that these blood miRNAs may be useful markers for discriminating patients with renal tumors from healthy controls (AUC=.750, AUC=.853 and AUC=.738, respectively). Conclusions: miRNAs in the circulation are relatively stable, very accessible, low invasive and easily testable biomarkers. Our results suggest let-7c, miR-200c and miR-31 as novel stable blood-based markers for renal cancer detection. This work was supported by Grants PI07/0477 from Fondo de Investigaciones Sanitarias (FIS), Instituto de Salud Carlos III.S. Díaz Prado is supported by an Isidro Parga Pondal research contract by Xunta de Galicia (A Coruña, Galicia, Spain). Cancer research in our laboratory is supported by the “Fundación do CHU A Coruña”.