Given the low response rate of anti-angiogenic agents, a step forward would be discovering predictive biomarkers to distinguish responders from non-responders. So far, several candidate miRNA biomarkers have been identified, but they emerged from small studies and should be confirmed in large prospective trials. Besides, there has been no unified control miRNAs for normalization in the analysis of circulating miRNA expression. A proposed solution to this problem may be the introduction of exogenous control .