微小RNA(microRNA, miRNA)是一类内源性小分子单链RNA，在细胞增殖、分化、凋亡尤其是肿瘤发生发展等生理病理过程中发挥重要作用。miR-21 是研究最早也是较特殊的miRNA 之一，其在几乎所有的实体肿瘤包括胰腺癌中高表达。miR-21 通过作用于靶基因调控胰腺癌发生发发展，在胰腺癌细胞增殖、分化、迁移、侵袭以及肿瘤耐药性等起发面关键作用，有望成为胰腺癌诊断、治疗以及判断预后的潜在的生物标志物，有着潜在的临床应用价值。
MicroRNAs (miRNAs) are a class of single-stranded, evolutionary conserved, noncoding RNA molecules,which play important roles in various physiological or pathological processes, such as cell proliferation, differentiation,apoptosis, and especially tumorigenesis. All of them, miR-21 is one of the first studied and most special miRNAs as it is over expressed in nearly all of soil tumors. miR-21 has been shown to regulate the progression of pancreatic caner by targeting tumor suppressor or oncogenes, playing a key role in cell proliferation, differentiation, migration, invasion and drug resistance of pancreatic cancer. Therefore, miR-21 will possibly be a potential biomarker for diagnosis, therapy and prognosis of pancreatic cancer, showing potentially clinical value.