The involvement of microRNAs in malignant transformation and cancer progression was previously grounded. The observations made by multiple published studies led to the conclusion that some of these small sequences could be eventually used as biomarkers for diagnosis/prognosis. This meta-analysis investigated whether microRNA-181 family members could predict the outcome of patients carrying different types of cancer. We searched the PubMed and Embase databases for studies evaluating the expression levels of miR-181a/b/c/d in patients with cancer, selecting the publications that assessed the relation between low and high levels of one of these four microRNAs and patients’ outcome. Hazard ratios (HRs) or risk ratios (RRs) were extracted from the studies, and random-effect model was performed to investigate the role of miR-181 in the outcome of these patients. The meta-analysis comprised 26 studies including 2653 cancer patients from 6 countries. The results showed significant association between the expression of miR-181 family members and colorectal cancer. Considering the heterogeneity of the pathologies, the analysis, including all types of cancer and the expression of all the miR-181 family members together, showed no association with distinct outcome (HR = 1.099, p = 0.435). When the analysis was performed on each microRNA separately, the expression of miR-181c was significantly associated with the outcome of patients with cancer (HR = 2.356, p = 0.011) and miR-181a expression levels significantly correlated with survival in patients with non-small-cell lung cancer (HR = 0.177, p < 0.05). This meta-analysis revealed evidence regarding the involvement of miR-181 family members in the outcome of patients with some types of cancer, according to their expression level.
