Expression analysis of microRNA as prognostic biomarkers in colorectal cancer.

microRNA (miRNA) based biomarkers have unique advantages due to their critical regulatory function, superior stability, and relatively small number compared to mRNAs. A number of miRNAs play key roles in colon cancer stem cell chemoresistance and have clinical potential as prognostic biomarkers. The purpose of this study is to systematically validate the prognostic potential of miRNAs in colorectal cancer. In this study, we validated the prognostic potential of a panel of miRNAs using 205 stage II, III, and IV colorectal cancer specimens by qRT-PCR analysis. We cross validated our results using The Cancer Genome Atlas (TCGA) database. Many of the miRNAs we investigated have been functionally validated to be important in contributing to chemoresistance to 5-fluorouracil (5-FU) based chemotherapy. We determined that miR-16 is the most consistent miRNA for expression normalization in colorectal cancer. We have validated several miRNAs (miR-15b, miR-215, miR-145, miR-192, let-7g) that are significantly associated with progression free survival (PFS) and/or overall survival (OS) of colorectal cancer patients independent of tumor stage and age at diagnosis. These 5 miRNAs are significantly associated with OS of colorectal cancer even after tumor location (left side vs. right side) is adjusted for. Furthermore, the prognostic value of let-7g for overall survival was independently validated using the RNA-Seq results from TCGA colorectal cancer database. These results, taken together, establish a solid foundation towards miRNA based precision management of colorectal cancer.