Tumor‐derived exosomes: Potential biomarkers and therapeutic target in the treatment of colorectal cancer

Colorectal cancer (CRC) is the third most common cause of cancer‐related death in men and women in many countries. Early detection of CRC helps to prevent the advanced stages of the disease, and may thereby improve the survival of these patients. A noninvasive test with high specificity and sensitivity is required for this. Exosomes are lipid bilayer membrane nanovesicles that are released into most body fluids and especially in the microenvironment of cancer. They carry various proteins, lipids, and nucleic materials such as DNA, RNA, messenger RNA (mRNA), and microRNA (miRNA), and may also alter the function of target cells. In this review, we aimed to describe the biogenesis, composition, function, and the role of tumor‐derived exosomes in cancer progression. Moreover, their applications in tumor diagnosis and treatment are described, with a particular focus on CRC. The early endosome is formed by endocytosis of phospholipid bilayer of the host cell's membrane. During the transformation of the early to late endosome, intraluminal vesicles are created by inward budding of endosome with the cytoplasm content such as genetic information and proteins. This endosome with multiple intraluminal vesicles is named the multivesicular body (MVB). Afterwards, the MVB fuses with the plasma membrane and releases intraluminal vesicles to the extracellular environment. These released vesicles are called exosomes. Alternatively, the MVB may bind to the lysosome for degradation. The target cell can uptake exosomes in various ways, including fusion with the plasma membrane, endocytosis, and binding to receptors on cell surface. The size of exosomes is 30–100 nm.