• Yunfeng Ding, Wanbo Wu, Zhihong Ma, Xia Shao, Ming Zhang, and Zhanwei Wang.
• Department of Breast Surgery, Huzhou Central Hospital, Affiliated Central Hospital HuZhou University, Huzhou, Zhejiang Province, China.
• Medicine (Baltimore). 2021 Jun 4; 100 (22): e25964e25964.

BackgroundThe latest global cancer data from 2020 shows that breast cancer has replaced lung cancer as the number one cancer in the world. Searching for new biomarkers of breast cancer has important clinical significance for early diagnosis, prediction of prognosis, and targeted therapy. MicroRNA-21 (miRNA-21) can be used as a new molecular marker for early diagnosis, prognosis, and treatment of tumors. However, the expression of miRNA-21 in breast cancer and its prognosis are not clear. Therefore, this study conducted a meta-analysis to further clarify the relationship between the expression of miRNA-21 in breast cancer and prognosis. At the same time, we carried out bioinformatics analysis to further analyze the possible molecular mechanism of miRNA-21, so as to provide potential clinical indicators for the diagnosis, treatment, and prognosis of patients.MethodsPubMed, Medline, Embase, Web of Science, Wanfang, Chinese Biomedical Literature Database, Chinese National Knowledge Infrastructure, and other databases were used to retrieve the published relevant literatures. Include the eligible research, extract the survival data hazard ratios and 95% confidence intervals and other information. STATA16.0 software was used for meta-analysis. Download the miRNA data of breast cancer through the Cancer Genome Atlas (TCGA) database and Gene Expression Omnibus (GEO) database. The data extracted for independent sample t test and ROC curve was drawn. OncomiR plotted the survival curve of miRNA-21 on the prognosis of breast cancer. The target genes of miRNA-21 were predicted, and the Gene Ontology (GO) function and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway were analyzed. STRING database and Cytoscape construct protein-protein interaction (PPI) network to obtain Hub gene. The correlation between the expression level of Hub gene in breast cancer and the abundance of immune cell infiltration was analyzed by TIMER database and verified by Kaplan-Meien plotter database.ResultsThe results of this meta-analysis will be submitted to a peer-reviewed journal for publication.ConclusionIn this study, meta-analysis and bioinformatics analysis were used to further explore the prognosis, mechanism, and related pathways of miRNA-21 in breast cancer.Ethics And DisseminationThe private information from individuals will not be published. This systematic review also should not damage participants' rights. Ethical approval is not available. The results may be published in a peer-reviewed journal or disseminated in relevant conferences.Osf Registration NumberDOI 10.17605/OSF.IO/R32A9.Copyright © 2021 the Author(s). Published by Wolters Kluwer Health, Inc.

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