Detecting microRNA (miRNA) in stool is a novel approach for colorectal cancer (CRC) screening. This study aimed to identify stool-based miRNA as non-invasive biomarkers for detection of CRC and adenoma.

A miRNA expression array covering 667 human miRNAs was performed on five pairs of CRC and two pairs of advanced adenoma tissues. The most up-regulated miRNAs were validated in 40 pairs of CRC tissues, 16 pairs of advanced adenoma tissues and 424 stool samples including 104 CRCs, 169 adenomas, 42 inflammatory bowel diseases (IBD), and 109 healthy controls. miRNA levels were followed-up after removal of lesions.

In an array analysis, miR-31 and miR-135b were the most up-regulated miRNAs in CRC and advanced adenoma as compared with their adjacent normal tissues (> 13-fold increase). In stool samples, level of miR-135b was significantly higher in subjects with CRC (P < 0.0001) or adenomas (P < 0.0001), but not in IBD patients compared with controls. miR-135b showed a significant increasing trend across the adenoma to cancer sequence (P < 0.0001). Levels of miR-31 were not significantly different among groups. The sensitivity of stool mR-135b was 78% for CRC, 73% for advanced adenoma, and 65% for any adenoma, respectively, with a specificity of 68%. No significant difference in miR-135b level was found between proximal and distal colorectal lesions. Stool miR-135b dropped significantly upon removal of CRC or advanced adenoma (P < 0.0001).

Stool-based miR-135b can be used as a non-invasive biomarker for the detection of CRC and advanced adenoma.