This study aims to characterize the clinical and pathological features of early-onset colorectal cancer (EO-CRC; diagnosis at age ≤50) and to identify factors associated with more advanced tumor stage. The investigators will compare patients with early-stage disease (high-grade intraepithelial neoplasia, carcinoma in situ [Tis], and T1) to those with later-stage disease (T2 and above) to identify characteristics predictive of advanced staging. Adults aged ≤50 years with a pathological diagnosis of colorectal cancer or high-grade intraepithelial neoplasia at Shenzhen Hospital, Southern Medical University between January 2016 and September 2025 will be eligible for inclusion if clinical, endoscopic, and pathology records are available. This retrospective observational study will use existing medical records; no experimental treatments or additional procedures will be performed. De-identified information will be extracted from medical records, including demographics, symptoms, lifestyle factors, laboratory tests, endoscopic and imaging findings, pathology reports, treatments received, and follow-up outcomes. Data will be handled securely, stored using subject codes, and analyzed to compare groups and to develop statistical models that identify independent risk factors for advanced tumor stage. Participation involves no direct contact or additional testing for participants and poses minimal risk because only previously collected, de-identified data are used. Findings may inform improvements in early detection, risk stratification, and management strategies for younger patients with colorectal neoplasia.

Inclusion Criteria:

• Age ≤ 50 years
• Pathologically confirmed colorectal neoplasia diagnosed at Shenzhen Hospital, Southern Medical University between 2016-01-01 and 2025-09-30, defined as colorectal cancer (any T stage) or high-grade intraepithelial neoplasia (HGIN).
• Available source documentation: complete or retrievable clinical record, endoscopy report, and pathology report sufficient to determine diagnosis and stage.
• De-identifiable data available for extraction (records can be coded and exported without direct identifiers).
• No requirement for additional patient contact (retrospective use of existing records with IRB-approved consent waiver or documented consent per ethics approval).

Exclusion Criteria:

• Secondary/metastatic colorectal tumor (colorectal involvement proven to be metastasis from another primary site).
• Prior history of other active malignancy within the last 5 years that could confound staging or outcomes, unless disease is in long-term remission and clearly documented.
• Insufficient documentation to determine pathological diagnosis or T stage (key pathology report missing or illegible).
• Critical data missing for primary outcome (e.g., pathology date or staging information) that cannot be resolved after source review.
• Duplicate records or irreconcilable data (same patient with conflicting identifiers/records that cannot be reconciled).
• Patients who received initial diagnostic or therapeutic care outside the study site with no accessible pathology or endoscopy reports at Shenzhen Hospital.

Patients aged ≤50 years with pathology-confirmed colorectal cancer (any T stage) or high-grade intraepithelial neoplasia (HGIN) diagnosed at Shenzhen Hospital, Southern Medical University between 2016-01-01 and 2025-09-30. This retrospective single-cohort study uses de-identified electronic medical records, endoscopy, imaging, and pathology reports to extract demographics, clinical presentation, lifestyle and family history, laboratory and tumor markers, endoscopic/imaging features, detailed pathology (location, size, differentiation, TNM/AJCC stage, LVI, molecular markers if available), treatments, and follow-up outcomes. No additional patient contact or study interventions; data handled under IRB approval/waiver with secure coding and restricted access.