Liquid Biopsy for Early Detection of Colorectal Cancer Using Circular RNA

Colorectal cancer (CRC) is the third most common malignancy and the second leading cause of cancer-related mortality worldwide. Despite the proven benefit of screening colonoscopy, its invasive nature, high cost, and low adherence rates limit its use for population-level early detection. Current non-invasive screening tools, such as fecal occult blood testing and stool DNA assays, offer limited sensitivity, particularly for early-stage or right-sided colorectal tumors. Therefore, there is a growing clinical need for a highly sensitive, minimally invasive, and patient-compliant diagnostic approach that can complement existing screening modalities. Circular RNAs (circRNAs) are a novel class of endogenous non-coding RNAs characterized by covalently closed loop structures formed through back-splicing. Unlike linear RNAs, circRNAs are resistant to exonuclease-mediated degradation and are remarkably stable in body fluids. They exhibit tissue- and cancer-specific expression patterns, suggesting strong potential as non-invasive biomarkers. Emerging evidence demonstrates that cell-free circRNAs (cf-circRNAs) circulate in plasma or serum either freely or encapsulated within extracellular vesicles such as exosomes. These cf-circRNAs retain the molecular signatures of their tumor of origin and can be reliably quantified using reverse transcriptase-quantitative PCR (RT-qPCR) or next-generation sequencing (NGS)-based platforms. The CIRCLED study (Circular RNA for Colorectal Cancer Detection) is designed as a multi-center, case-control, observational study aiming to (1) identify diagnostic circRNA candidates from RNA sequencing, and (2) validate a cf-circRNA diagnostic panel capable of differentiating CRC patients from healthy individuals and those with benign colorectal diseases.