To sum it up, promoted mir-21 level in cancer tissues was related to greater risk of relapse and mortality while the predictive force of circulating mir-21 only applied to OS given the analysis of available studies. Since the initial recognition of the association of mir-21 with cancer in 2005, mir-21 has stood out as the most extensively explored miRNAs. Recent studies involving cancer cell lines and xenograft models have implicated the oncogenic role of mir-21. Accumulating evidence has supported mir-21 as a potential diagnostic and prognostic biomarker in various carcinomas. In our meta-analysis study, it was Chloramphenicol preliminarily concluded that mir-21 level facilitated the prediction of long-term survival in cancers including NSCLC and pancreatic cancer, which further validated the prognostic value of this oncomir. As a matter of fact, the noteworthy association between aberrant mir-21 expression and poor survival could be best illuminated by its indispensable role in carcinogenesis and metastatic cascade. Latest findings have shed light upon the underlying oncogenic mechanisms of mir-21, Dinotefuran which exerted profound influence over the basic hallmarks of cancer, including cell proliferation, apoptosis, differentiation, invasion and migration. The mir-21 gene is located on chromosome 17q23.2 within the common fragile site FRA17B, which is frequently observed to be amplified in numerous malignancies. Of great importance, the oncogenic effect of mir-21 could be primarily explained by its transcriptional targets and downstream signal pathways. So far, validated targets of mir-21 included programmed cell death 4 gene, tropomyosin 1, phosphatase and tensin homolog, chromosome condensation protein G, reticulon 4 isoform A and other cancer-related genes. Altogether, the vital cellular pathways regulating cell proliferation, apoptosis and cell cycle such as Ras, p53, PI3K-Akt-mTOR pathway, as well as target genes compose an intricate network of mir-21 modulation.