Thom Bongaerts

81 Attendance characteristics of the breast and colorectal CSPs Methods A retrospective observational study was performed among all screening-eligible people concerning the BC-SP and the CRC-SP living in The Hague, the Netherlands, between 2005 to 2019. Screening programmes in the Netherlands The Netherlands hosts CSPs aimed at cervical, breast and CRC. Screening participation is on a voluntary basis, and the screening tests are offered free of charge by the Dutch government.5 The BC-SP invites women between 50-75 years of age and uses a bilateral mammography as screening tool. After a an abnormal screening result the participant will be referred to the hospital by the general practitioner (GP).6 The CRC-SP invites both women and men aged between 55-75 years and uses a faecal immunochemical test (FIT) as screening tool. After a positive FIT, participants will be scheduled for a coloscopy in a contracted colonoscopy centre by the screening organization.7 Data management In the Netherlands, The National Institute for Public Health and the Environment (Rijksinstituut voor Volksgezondheid en Milieu, RIVM) and the national screening organisation are in charge of organizing and coordinating the CSPs. Detailed data on national participation rates are publicly available through the RIVM website.5 Regional screening invitation and attendance data were retrieved via the national screening organisation, region South-West (Bevolkingsonderzoek Zuid-West, BVO-ZW). Cancer incidence data were retrieved from the Netherlands Cancer Registry (NCR) via the Netherlands Comprehensive Cancer Organisation (Integraal Kankercentrum Nederland, IKNL).18 Both datasets were linked on an individual level by IKNL after approval from the privacy officers of both organisations. On forehand the Ethics Committee of the Leiden University Medical Centre issued a waiver of consent (G18.096). At time of the data extraction (2020), most recent complete datasets were extracted relating to the screening data of BVO-ZW. For the BC-SP extracted data was from 2005 to 2019. For the CRC-SP extracted data was from 2014 to 2019. Since the CRC-SP was only fully integrated and functioning from 2019, included data was of the implementation phase of the CRC-SP. The BVO-ZW-database contained the variables: gender; year of birth; 4-digit zip code, tests results: mammography and colonoscopy. The NCR-database contained the 3

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