We clarified the predictive and prognostic value of circulating plasma exosomal microRNA-21 (miR-21) in each TNM stage of colorectal cancer (CRC) patients.

The microRNA (miRNA) profiles of the plasma exosomes, primary tumor tissues, and liver metastasis tissues from the same CRC patients were examined using a microarray. For validation analysis, the plasma exosome samples from 326 CRC patients were measured by TaqMan miRNA assays.

In the miRNA microarray analyses, miR-21 showed the highest upregulation in exosomes, primary tumor tissues, and liver metastasis tissues. Significant correlations were demonstrated between exosomal miR-21 and tissue miR-21 levels. As for the relationship to the pathological condition, exosomal miR-21 showed a significant association with liver metastasis and TNM stage. The overall survival (OS) rates and disease-free survival (DFS) rates in high-exosomal-miR-21 patients were significantly worse than those in low-miR-21 patients. Exosomal miR-21 levels were an independent prognostic factor for OS and DFS in CRC patients with TNM stage II or III, and for OS in patients with TNM stage IV.

Plasma exosomal miR-21 levels are a useful biomarker for the prediction of recurrence and poor prognosis in CRC patients with TNM stage II, III, or IV.