How to define exosome? Exosomes are secreted microvesicles that are functionally active and can transmit information between cells. Nowadays, more and more researchers have focused their attention on the role of exosomes in the occurrence and development of tumors and their clinical application.

Nucleic acid molecules such as miRNA, mRNA, long non-coding RNA (lncRNA) and DNA carried in exosomes secreted by tumor cells are the most concerned class of molecules that can be used as biomarkers for tumor diagnosis. These molecules reflect the physiological status and functional status of secretory cells, and will even contain the molecular information related to cell morbidity, especially the miRNAs contained in exosomes derived from tumor cells are heterogeneous, which makes exosome-derived miRNAs potentially a new indicator for tumor diagnosis. Exosome contents are numerous and complex. Recent studies have shown that the DNA, mRNA and lncRNA in exosomes secreted by tumor cells can reflect the pathophysiological status of tumor patients and the nature of primary tumors, and are expected to be used as indicators for the diagnosis of tumors.

Respiratory Tumors

A research on lung adenocarcinoma patients, lung granuloma patients, and healthy smokers showed that four miRNAs in plasma exosomes could be used for the screening of lung cancer, and another six miRNAs could be used for the diagnosis of lung cancer. The miRNA expression profile in exosomes from non-small cell lung cancer (NSCLC) was different from that in normal tissues, in which the expression levels of let7f and miRNA-30e-3p could distinguish between patients with early and advanced NSCLC, and the expression levels of both were associated with poorer prognosis of patients. Thus, circulating exosome-derived miRNAs may be used as non-invasive biomarkers for the early diagnosis of lung cancer.

Tumors of the Digestive System

miRNA-21, the exosome RNA, was significantly higher in patients with malignant esophageal squamous cell carcinoma than in patients with benign reflux esophagitis, and high expression of exosomal miRNA-21 often predicted extensive invasion of cancer cells and cancer recurrence. In a study, four miRNAs were specifically and highly expressed in exosomes from pancreatic cancer patients, but were rarely expressed in normal controls. Exosomes have important clinical value in digestive system tumors and have broad application prospects.

Urinary System Neoplasms

By analyzing exosomes from blood and urine of prostate cancer patients and normal controls, it’s reported that miRNA-141 and miRNA-375 may be used as exosome marker for the diagnosis of prostate cancer. The mRNA of exosomes in urine can be used to differentiate prostate cancer from benign proliferative diseases, and the genetic test of exosomes in urine can be used instead of pathological biopsy to differentiate prostate cancer from diseases with elevated prostate specific antigen alone.

Reproductive System Neoplasms

The miRNA profiles of exosomes in the blood of ovarian cancer patients were significantly different from those of normal individuals, and eight miRNAs were significantly increased in exosomes from the serum of ovarian cancer patients, suggesting that exosomes are helpful in the diagnosis of ovarian cancer. Another study showed that exosomal miRNA-1246 and miRNA-21 expression in plasma was significantly higher in breast cancer patients than in healthy controls (P = 0.03, 0.04, respectively), indicating that miRNAs in exosomes can be used for the diagnosis of reproductive system tumors.

Other tumors

In studies of tumors in other systems, researchers compared serum exosomes from patients with malignant brain glioblastoma and normal controls and screened the most differentially expressed miRNA-574-3p, miRNA-320, and RNU6-1 using microarray technology, and also confirmed that RNU6-1 alone or in combination with multiple miRNAs can specifically diagnose malignant glioblastoma. The results showed that miRNA-15a expression was significantly downregulated in exosomes from bone marrow mesenchymal stem cells of multiple myeloma patients, which was closely related to the characteristics of multiple myeloma.

Nucleic acid molecules present in circulating exosomes have the possibility to be used as early exosome diagnostic markers of tumors, and although the specific mechanism of action remains to be studied in depth, they have shown great potential in the clinical diagnosis of various tumors. More and more researchers are working on amplifying this molecule in circulating body fluids to make it a diagnostic tool, thereby facilitating the development of tumor liquid biopsies and opening a new door for the early diagnosis of tumors.

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