[Circulating MicroRNAs as Biomarkers of Colorectal Cancer]

Colorectal cancer is a common tumor in Japan, causing almost 50,000 deaths per year. The development of new biomarkers is strongly desired, in order to detect the early stage of colorectal cancer with high sensitivity and specificity, using less invasive and high through-put methods. miRNA is a small non-coding RNA which regulates gene expression by digesting mRNA or suppressing translation. miRNAs are stable and present in blood, urine, stool, and other body fluids. The profiles of miRNAs in body fluid are specific to pathological states. There is accumulating data showing the usefulness of miRNAs as new biomarkers for colorectal cancer. We summarize the current knowledge in the previous literature (10 plasma analyses: sensitivity: 83.3 to 89%, specificity: 41 to 84.7%, AUC: 0.606 to 0.896; 13 serum analyses: sensitivity: 66.7 to 96.4%, specificity: 63.9 to 88.1%, AUC: 0.679 to 0.918; and 8 fecal analyses: sensitivity: 70.9 to 81.8%, specificity: 68.4 to 96.3%, AUC: 0.64 to 0.829). We focus on the standardization of miRNA analysis, namely: 1) preanalytical processes: difference of miRNA levels between plasma and serum, sampling methods, preparation of plasma or serum, and preservation of samples; 2) analytical processes: mRNA extraction methods, amplification, normalizer, and cut-off values. In conclusion, miRNAs are expected to become new biomarkers for colorectal cancer screening.