Abstract: MicroRNAs (miRNAs) are a group of endogenous small noncoding RNAs, approximately
21～25 nucleotides in length. In mammals, their function is mainly repressing the mRNA transcripts via
imperfect complementary sequences in the 3’-UTR of target mRNAs. miRNAs play important roles in many
physiological and pathological processes. Over the past decades, overwhelming studies have reported that
miRNAs are associated with the proliferation and apoptosis of tumor cells. miRNAs aberrantly expressed in
tumor tissues have significant roles in tumor induction, progression and recurrence. Depending on miRNA
function and status in cancer, miRNAs are generally classified as tumor suppressor or onco-miRNAs. In
addition to the deregulated expression levels and potentially mutations that altering a miRNA seed sequence
could ablate target repression by tumor-suppressive miRNAs or allow for altered target selection, which could
contribute to oncogenesis. In this review, an overview on the miRNAs study in primary liver cancer were
given so as to provide useful clues to understand the significance of miRNAs in the future.