Upregulation of microRNA-31 is associated with poor prognosis in patients with advanced colorectal cancer

Colorectal cancer (CRC) manifests after the accumulation of genetic and epigenetic alterations along with tumor microenvironments. MicroRNA (miRNA/miR) molecules have been revealed to serve in critical roles in the progression various types of cancer, and their expression level is often an important diagnostic, predictive or prognostic biomarker. The aim of the present study was to evaluate the potential of miRNAs as prognostic biomarkers for patients with advanced CRC. miRNA arrays were performed on CRC specimens obtained from tumors with various molecular statuses [e.g. KRAS proto-oncogene, GTPase (KRAS)/B-Raf proto-oncogene, serine/threonine kinase (BRAF)/microsatellite instability (MSI)], and their paired normal mucosal specimens. The miRNA array revealed that miR-31-5p (miR-31) was specifically upregulated in CRCs with the BRAF V600E mutation, the results of which were supported by subsequent analysis of a dataset retrieved from The Cancer Genome Atlas (TCGA) database, which contained information regarding 170 patients with CRC including 51 BRAF-mutant CRCs. Of our cohort of 67 patients with stage IV CRC, 15 (22%) and 4 (6%) showed KRAS and BRAF V600E mutations, respectively. Since the median miR-31 expression was 3.45 (range, 0.004–6330.531), the cut-off value was chosen as 3.5, and all tumors were categorized into two groups accordingly (high-/low-miR-31 expression). The high miR-31 expression group (n=33) was significantly associated with a poorer mortality (univariate hazard ratio=2.12; 95% confidence interval, 0.23–0.95; P=0.03) and exhibited a shorter median survival time (MST; 20.1 months) compared with the low miR-31 expression group (n=34) (MST, 38.3 months; P=0.03), indicating that miR-31 is a promising prognostic biomarker for patients with advanced CRC. Thus, performing a functional analysis of miR-31 expression may lead to the development of new targeted therapies for the various genetic subtypes of CRC.