Despite the development of therapeutic strategies, cancer is the second death cause worldwide and still rising. Unclear molecular mechanisms of carcinogenesis and lack of biomarkers for early diagnosis or advanced management are responsible for the poor prognosis of cancer. Recently, exosomes have been the focus of tumor studies, as they carry many biomolecules including proteins, lipids, and nucleic acids, and transfer them to participate in tumor development. Among the biomolecules, noncoding RNAs including microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs) in exosomes have been found to participate in carcinogenesis and gain more attention. Compared with lncRNAs and miRNAs, the exosomal circRNAs are less studied in tumor studies. However, circRNAs are enriched and more stable in exosomes because of their covalently closed‐loop structures, protection provided by exosomes, and protein binding partners. Furthermore, exosomal circRNAs display more potent sponge effect for miRNAs, as they contain more miRNA response elements than lncRNAs. In this review, we highlighted the functional roles of exosomal circRNAs on the tumor progression including tumor growth, invasion, metabolism, immunomodulation, and chemotherapeutic drug resistance. Moreover, we also summarized predictive potency and clinical use of exosomal circRNAs in cancer.

中文翻译：

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外体环状RNA在癌症中的作用

尽管发展了治疗策略，但是癌症是全球第二大死亡原因，并且仍在上升。致癌的分子机制不清楚，缺乏早期诊断或先进治疗的生物标志物，是导致癌症预后不良的原因。最近，外来体一直是肿瘤研究的重点，因为外来体携带许多生物分子，包括蛋白质，脂质和核酸，并转移它们参与肿瘤的发展。在生物分子中，已发现外泌体中的非编码RNA（包括microRNA（miRNA），长非编码RNA（lncRNA）和环状RNA（circRNA））参与了致癌作用并引起了更多关注。与lncRNA和miRNA相比，外泌体circRNA在肿瘤研究中的研究较少。然而，由于circRNA的共价闭环结构，外泌体提供的保护以及蛋白质结合伴侣，因此它们在外泌体中富集且更稳定。此外，外泌体circRNA对miRNA表现出更强的海绵效应，因为它们比lncRNA包含更多的miRNA反应元件。在这篇综述中，我们强调了外体circRNA在肿瘤进展中的功能作用，包括肿瘤生长，侵袭，代谢，免疫调节和化学治疗药物抗性。此外，我们还总结了外泌体circRNA在癌症中的预测效力和临床应用。我们强调了外泌体circRNA在肿瘤进展中的功能作用，包括肿瘤生长，侵袭，新陈代谢，免疫调节和化疗药物耐药性。此外，我们还总结了外泌体circRNA在癌症中的预测效力和临床应用。我们强调了外泌体circRNA在肿瘤进展中的功能作用，包括肿瘤生长，侵袭，新陈代谢，免疫调节和化疗药物耐药性。此外，我们还总结了外泌体circRNA在癌症中的预测效力和临床应用。