Background: Population-based colorectal cancer (CRC) screening using stool-based blood testing and/or colonoscopy constitutes a cornerstone in CRC prevention and has been widely implemented in high-income countries. These screening programs identify a substantial number of individuals with precancerous lesions, predominantly colorectal polyps, which are removed during colonoscopy. These individuals remain at increased risk of polyp recurrence and progression to CRC and are therefore typically monitored with repeated colonoscopies. Gaining deeper insight into preventive measures for this high-risk group has the potential to enhance the effectiveness and long-term impact of CRC screening programs.

Objectives: The aim of this project was to establish a cohort of CRC screening participants undergoing colonoscopy, to enable identification of lifestyle, dietary, and medical risk factors for polyp recurrence and CRC in a high-risk population with polyps detected through CRC screening.

Methods: The “POLLY–prevention of polyps and colorectal cancer” cohort was established in 2019 and comprises participants from the Danish national CRC screening program who were referred to colonoscopy based on a positive stool-based blood test and underwent a complete colonoscopy. Eligible individuals were identified and invited by their regional screening secretariat three weeks after colonoscopy. Participants completed three web-based questionnaires: 1) a food frequency questionnaire, 2) a lifestyle questionnaire, including information on drug use, and 3) a patient-reported outcome questionnaire assessing experiences with the screening procedures and potential complications. The Danish CRC screening program provided a unique setting with its systematic surveillance of individuals at increased CRC risk, while the comprehensive Danish nationwide registries enabled ascertainment of recurring colorectal polyps and incident CRC. Enrollment into the cohort will continue through March 2026.

Results: By the end of 2025, a total of 52,637 men and women had been invited to participate in the POLLY cohort, and 12,561 accepted the invitation. Characteristics of the cohort, including key demographic, dietary, and lifestyle factors, as well as measures of polyp and CRC burden, will be presented at the conference.

Conclusions/Implications: Identification of modifiable risk and protective factors associated with polyp recurrence and CRC may inform the development and refinement of targeted preventive recommendations for high-risk individuals identified by screening. Thus, the POLLY cohort constitutes a valuable resource with substantial potential to enhance the effectiveness of CRC screening programs.