Approximately 30-50% of colorectal cancer (CRC) patients who undergo curative resection subsequently experience tumor recurrence or metastasis. Although microRNAs (miRNAs) are a class of small noncoding RNAs frequently deregulated in various human malignancies, it remains unknown if these can help predict recurrence and metastasis in CRC patients. MiRNAs were initially screened using miRNA-microarray and miRNA-seq datasets with or without recurrence. Candidate miRNAs were then tested in two independent cohorts of 111 stage II/III and 139 stage I-III CRC patients, as well as serum samples and matched primary and metastatic liver tissues. An animal model of peritoneal dissemination was used to assess the oncogenic role of the target miRNA. Four candidate miRNAs were identified during the initial screening, and we subsequently validated upregulation of miR-139-5p in two independent clinical cohorts, wherein it associated with poor recurrence-free survival. Moreover, miR-139-5p were also upregulated in the serum of recurrence-positive CRC patients and yielded significantly shorter recurrence-free survival. Intriguingly, miR-139-5p was upregulated in metastatic liver tissues and negatively correlated with genes associated with epithelial-mesenchymal transition. Lastly, we showed that miR-139-5p overexpression enhanced peritoneal dissemination in a mouse model. In conclusion, we identified miR-139-5p as a novel biomarker for tumor recurrence and metastasis in CRC.
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