An Ambidirectional Cohort Study on Colorectal Adenoma

This is a single-center, ambidirectional cohort study conducted at the Second Affiliated Hospital of Zhejiang University School of Medicine, aiming to develop and validate a risk prediction model for colorectal adenoma recurrence and progression. The design includes both a retrospective component, which enrolls patients treated in the past 10 years with existing clinical data, and a prospective component, which enrolls patients from the date of ethical approval until December 31, 2030. No sampling frame is applied; all patients meeting the eligibility criteria will be consecutively enrolled until the target sample size of 1,280 participants is achieved. The retrospective cohort will provide preliminary data for model calibration, while the prospective cohort will serve for model development and temporal validation.

This study operates as a patient registry with embedded quality assurance mechanisms. Although the registry is not certified by a third party, internal quality control follows standardized operating procedures aligned with institutional review board requirements and Good Clinical Practice principles for observational studies. A formal quality assurance plan has been established to address data validation and registry procedures. Regular on-site monitoring visits are conducted quarterly by an independent data monitor not involved in patient recruitment or data entry, assessing adherence to the protocol, completeness of case report forms, and consistency with source documents. Annual internal audits are performed by the hospital's clinical research audit unit to evaluate compliance with data management standard operating procedures, patient confidentiality protections, and biospecimen handling protocols. External audits are not planned unless required by the funding agency or regulatory authority.

Data entered into the registry undergo multiple automated and manual checks. Range checks validate continuous variables against predefined normal or plausible ranges, with out-of-range values flagged for review. Consistency checks verify cross-field consistency, such as ensuring that the date of adenoma resection precedes the date of first follow-up colonoscopy and that smoking status changes follow logical sequences. Logical checks apply internal rules, such as the number of adenomas not being negative and follow-up intervals aligning with risk categories. Duplicate detection algorithms identify potential duplicate patient records based on medical record number, date of birth, and name initials. All flagged discrepancies are resolved by querying the responsible study coordinator and verifying against source documents, with corrections documented with audit trails.

Source data verification is performed on a random sample of 20% of enrolled participants, comparing registry data against external source documents including electronic medical records, paper or electronic case report forms, laboratory information systems, and biospecimen tracking logs. For the retrospective cohort, additional verification compares extracted data against original hospital records. For the prospective cohort, a subset of 10% of participants undergoes full source data verification, with an additional targeted verification for primary outcome events such as adenoma recurrence, advanced adenoma, and colorectal cancer. The acceptable accuracy threshold is set at 98% or higher agreement for critical variables and 95% or higher for non-critical variables.

A comprehensive data dictionary is maintained and version-controlled. For each variable, the dictionary includes the variable name and full label, definition and description, data type, allowed values or valid range, source of the variable, coding schemes where applicable (such as MedDRA version 26.0 or later for medical history and adverse events, WHO Drug Dictionary Global for concomitant medications, and WHO classification of tumors of the digestive system for adenoma morphology), normal ranges for laboratory parameters, missing value codes, and time of collection. The data dictionary is accessible to all study personnel and is updated as needed, with version control and change logs maintained.