Candidate microRNA biomarkers in human colorectal cancer: systematic review profiling studies and experimental validation.

Colorectal cancer (CRC) is a major cause of cancer mortality worldwide. There is an urgent need to search for specific and sensitive biomarkers for early diagnosis of CRC. We carried out a comprehensive systematic review of published studies that compared the miRNA expression profiles between CRC tissue and paired neighboring noncancerous colorectal tissue to determine candidate miRNA biomarkers for CRC. A miRNA ranking system that takes the number of comparisons in agreement, total study sizes and direction of differential expression into the consideration was devised and used. One of the most up-regulated miRNAs, miRNA-106a, was consistently reported to be differentially expressed in six studies and the five most down-regulated miRNAs, miR-30a-3p, miR-139, miR-145, miR-125a and miR-133a, were consistently reported to be differentially expressed in four studies. Moreover, we further validated five miRNAs in a clinical setting using qRT-PCR, which demonstrated that miR-106a expression was increased, whereas the expression of miR-30a-3p, miR-145, miR-125a and miR-133a was decreased in the CRC tissues. Therefore, these miRNAs may be the candidates to develop a panel of biomarkers with sufficient sensitivity and specificity for the diagnosis of CRC in a clinical setting.