Colorectal cancer (CRC) is a leading cause of cancer-related deaths worldwide. This study aims to develop a non-invasive liquid biopsy assay using plasma-derived cell-free circular RNAs (cf-circRNAs) for early and accurate detection of colorectal cancer.

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.

Inclusion Criteria:

• Adults (≥18 years old)
• Histologically confirmed colorectal cancer (Stage I-III)
• Availability of pre-treatment plasma samples
• Written informed consent provided

Exclusion Criteria:

• History of other active malignancies within the past 5 years
• Poor sample quality or hemolysis
• Inability to provide informed consent

Patients with histologically confirmed colorectal adenocarcinoma (Stages I-III) Patients with benign colorectal diseases (adenoma, polyp) Healthy control individuals with no evidence of malignancy

Data collected for the study will be made available to others, including de-identified participant data, at publication, via a signed data access agreement and at the discretion of the investigators' approval of the proposed use of such data