MicroRNAs (
miRNAs) are 18- to 22-nucleotide-long, single-stranded, noncoding RNAs that regulate important biological processes including differentiation, proliferation, and response to cellular stressors such as
hypoxia, nutrient depletion, and traversion of the cell cycle by controlling
protein expression within the cell. Many investigators have profiled
cancer tissue and serum
miRNAs to identify potential therapeutic targets, understand the pathways involved in
tumorigenesis, and identify diagnostic
tumor signatures. In the setting of
pancreatic cancer, obtaining pancreatic tissue is invasive and impractical for early diagnosis. Several groups have profiled
miRNAs that are present in the blood as a means to diagnose
tumor progression and predict prognosis/survival or drug resistance. Several
miRNA signatures found in pancreatic tissue and the peripheral blood, as well as the pathways that are associated with
pancreatic cancer, are reviewed here in detail. Three
miRNA biomarkers (miR-21, miR-155, and miR-200) have been repetitively identified in both
pancreatic cancer tissue and patients' blood. Those
miRNAs regulate and are regulated by the central genetic and epigenetic changes observed in
pancreatic cancer including p53,
transforming growth factor β,
p16(INK4A), BRCA1/2, and Kras. These
miRNAs are involved in DNA repair, cell cycle, and cell invasion and also play important roles in promoting
metastases.