Role of miRNA in transformation from normal tissue to colorectal adenoma and cancer.

Although many modalities can be used to prolong the remission of colorectal cancer (CRC), early diagnosis is essential to improve the therapeutic outcomes. The conventional ways of diagnosing and monitoring the progresses from adenoma to CRC are colonoscopy and fecal occult blood test (FOBT). However, colonoscopy is expensive and invasive; while the FOBT is not sensitive. miRNAs may be a new modality to monitor the transition from adenoma to CRC. We reviewed publications of miRNA profile differences from colorectal normal mucosa (NM) to adenoma, and to CRC and tried to find the roles of miRNA in these transitions. This review also highlighted the possibility of serum miRNAs as markers for monitoring these transitions. The miRNA profiles are different from normal colorectal mucosa to adenoma and to CRC. The miRNAs may have pro- or anti-CRC effects through oncogenes such as c-Met and KRAS. Others may interfere with the immune system. More interestingly, some miRNAs are continuously increased from NM to adenoma and to CRC; others, such as miRNA-30b, are consequently decreased. The literature shows that miRNAs are involved in the whole process of the colorectal carcinogenesis. The miRNAs may be the biomarkers in monitoring the transition from adenoma to CRC.