Importance of Extracellular Vesicle Derived RNAs as Critical Colorectal Cancer Biomarkers

Abstract

Colorectal cancer typically begins from a nonmalignant polyp formation in the large intestine that, over time, develops into colorectal cancer. The growth of benign polyps can be checked if detected in the early stages of the disease. Doctors usually recommend colonoscopy to average and high-risk individuals for colorectal cancer screening. Elevated carcinoembryonic antigen (CEA) is a broadly used biomarker for colorectal cancer. The genetic and epigenetic alteration of genes such as p53, BRAF, APC, and PIK3CA is also correlated with colorectal cancer in various clinical studies. In general, tissue biopsy is most frequently used for colorectal cancer diagnosis, but the whole tumor heterogeneity cannot be accessed by this technique. Furthermore, such a highly invasive technique is not suitable for repeated testing. Recently, extracellular vesicles (EVs), lipid bilayer enclosed sacs secreted from colorectal cancer cells, are emerging as a diagnostic tool for colon cancer detection. The major advantages of using EVs for colon cancer diagnosis are (i) EVs can be isolated in a noninvasive manner from the body fluid and (ii) EV incorporated cargoes (mostly RNAs) reveal various aspects of colorectal cancer. EV-RNAs are also implicated in tumor invasion and influence the immune system for the further spread of tumors. However, due to the lack of standardized EV detection strategies, diagnostic applicability is limited. Herein, we review the recent literature on the pathobiological dependence of colorectal cancer on EV-RNAs. Further, we present the advantages of identification and characterization of EV-RNAs to explore the connection between differential expression of extracellular vesicle incorporated RNAs and colorectal cancer. How this approach may potentially translate into point of care colorectal cancer diagnostics is also discussed.