外泌体循环RNA在肿瘤的发展和进展中发挥关键作用，可能是各种癌症诊断和治疗的新生物标记物。然而，外泌体循环RNA在乳腺癌中的生物功能和临床意义尚不清楚。本研究利用exoRBase 2.0数据库中的外泌体循环RNA表达谱鉴定了乳腺癌患者中的差异表达外泌体循环RNA。采用LASSO和SVM-RFE算法并进行多元 logistic 回归分析构建协助诊断模型。使用差异表达分析、CSCD、TargetScan和ENCORI数据库选择circRNA的靶基因。进行单变量和多元生存分析，建立一个与外泌体循环RNA-miRNA-mRNA相关的生存网络，并使用GSVA和CIBERSORT算法评估乳腺癌的癌症标志物和免疫细胞，并使用Spearman相关分析调查它们与circRNA-miRNA-mRNA网络的相关性。 在乳腺癌患者中鉴定出347个上调和3个下调的外泌体循环RNA。基于14个外泌体循环RNA的诊断模型在训练（AUC=0.98）和验证的数据集中表现出很高的曲线下面积（AUC=0.94）。共选择70个miRNA和1147个mRNA作为circRNA的下游靶点，并揭示参与肿瘤相关通路，包括PI3K-AKT、MAPK、RAS 和 RAP1 通路、钙信号通路和转录失调。构建的外泌体循环RNA-miRNA-mRNA相关的生存网络包含9个外泌体循环RNA、12个miRNA和10个mRNA，显示出复杂的相关性和相互作用。与circRNA-miRNA-mRNA网络密切相关的癌症标志物通路包括TGF-β、KRAS 和 MYC信号通路、肿瘤血管生成、上皮-间质过渡、DNA修复和G2M检查点，与之相关的免疫细胞包括CD4+和CD8+ T细胞、树突状细胞、肥大细胞、巨噬细胞、记忆B细胞和自然杀伤细胞。 本研究是首次系统分析乳腺癌中的外泌体循环RNA。我们建立了外泌体循环RNA诊断模型，构建了一个相关的外泌体循环RNA-miRNA-mRNA生存网络。结果揭示了外泌体循环RNA-miRNA-mRNA网络在乳腺癌中的复杂功能和潜在机制，需要进一步验证。本文受版权保护，所有权利均归作者所有。

Exosomal circRNAs played critical roles in tumor development and progression and might be novel biomarkers in the diagnosis and treatment of various cancers. However, the biological functions and clinical implications of exosomal circRNAs in breast cancer are unclear.Expression profiles of exosomal circRNAs in exoRBase 2.0 database were used to identify differentially expressed exosomal circRNAs in breast cancer. The LASSO and SVM-RFE algorithm followed by multivariate logistic regression analysis were performed to construct the diagnostic model. The target genes of circRNAs were selected by combing differential expression analysis and CSCD, TargetScan and ENCORI database. Univariate and multivariate survival analysis were conducted to construct a survival-associated exosomal circRNA-miRNA-mRNA network. GSVA and CIBERSORT algorithm were used to evaluate the cancer hallmarks and immune cells in breast cancer and spearman correlation analysis was used to investigate their correlations with the circRNA-miRNA-mRNA network.A total of 347 upregulated and 3 downregulated exosomal circRNAs were identified in breast cancer patients. The diagnostic model basing on 14 exosomal circRNAs showed a high area under the curve (AUC) value in both the training (AUC = 0.98) and validation dataset (AUC = 0.94). A total of 70 miRNAs and 1147 mRNAs were selected as the downstream targets of circRNAs and were revealed to participate into tumor-associated pathways including PI3K-AKT, MAPK, RAS and RAP1 pathways, calcium signaling pathways and transcriptional misregulations. The constructed survival-associated exosomal circRNA-miRNA-mRNA network contained 9 exosomal circRNAs, 12 miRNAs and 10 mRNAs and showed complicated correlations and interactions within networks. Cancer hallmark pathways including TGF-β, KRAS and MYC signaling pathways, tumor angiogenesis, epithelial-mesenchymal transition, DNA repair and G2M checkpoint and immune cells including CD4+ and CD8+ T cells, dendritic cells, mast cells, macrophage cells, memory B cells and natural killer cells were closely correlated with the circRNA-miRNA-mRNA network.Our study was the first to systematically analyze the exosomal circRNAs in breast cancer. We established an exosomal circRNA diagnostic model and constructed a survival-associated exosomal circRNA-miRNA-mRNA network. Our results revealed the complicated functions and potential mechanisms of exosomal circRNA-miRNA-mRNA network in breast cancer which need to be further validated in the future.This article is protected by copyright. All rights reserved.