Fecal microRNAs as non-invasive biomarkers for the detection of colorectal cancer: A systematic review

INTRODUCTION: Colorectal cancer (CRC) is currently still one of the most frequent cancers worldwide. Even if the available screening tests have helped to reduce incidence and mortality for this cancer, new potential biomarkers to use in concomitance could improve effectiveness of CRC detection. microRNAs (miRNAs) are the most famous class of small non-coding RNAs which regulate several biological processes. They are stable and easily detectable in different biospecimens and their expression has been reported dysregulated in many diseases, including CRC. Stool miRNAs, in particular, seem really interesting as potential noninvasive diagnostic CRC biomarkers. EVIDENCE ACQUISITION: We have systematically reviewed all the studies investigating miRNAs dysregulation in stool in relation to CRC. Nineteen different works were included in the present review. EVIDENCE SYNTHESIS: The retrieved studies mostly investigated fecal miRNA expression levels (often together with tumor/healthy tissues, and in a couple of studies, also in plasma/serum) by RT-qPCR or microarray. Globally, 51 miRNAs were reported as dysregulated in CRC patients compared to controls: 32 up-regulated and 19 down-regulated. Among them, miR-106a, miR-17, miR-18a, miR-20a, miR-21, miR-92a, miR-96, miR-223 and miR-143 expression levels have been described as altered by more than two studies. CONCLUSIONS: The relatively few available studies so far demonstrate the feasibility and a good potentiality of non-invasive stool miRNA-based test for the detection of CRC, reflecting same altered expression as in primary tissue. For this reason, the whole miRNome needs to be exhaustively explored in human stool samples with further investigations on larger study populations of CRC cases and controls.