Subsequent participation in organized FIT based screening following screen-derived colonoscopy

Introduction: In the Danish National Colorectal Cancer (CRC) screening program, participants with screen-detected low-risk adenomas are invited to a new faecal immunochemical test (FIT) screening after two years. However, participation rate in next FIT screening is unknown. We aimed to investigate this subsequent participation rate within the Danish CRC screening program. Methods: This nationwide register-based study included participants aged 50-72 years registered with FIT screening in the Danish CRC screening program between January 1, 2016, and June 30, 2017. Participants were included if their index FIT was negative or if it was positive and the subsequent colonoscopy detected low-risk adenomas. Invitees were categorized as subsequent participants if they returned a FIT within 135 days following the invitation to screening. We estimated the relative risk for participation depending on screening outcome, age, and sex. Result: 415,107 with a negative result and 5,550 with low-risk adenomas were included. 86.0% (85.9;86.1) of the invitees with a negative result participated in the subsequent screening, while 71.8% (70.6;73.0) of the invitees with low-risk adenomas participated subsequently. The risk of participation in the subsequent screening was significantly lower among all age groups of men and women with low-risk adenomas compared to similar groups with negative results. Conclusion: Invitees with low-risk adenomas detected at their initial colonoscopy are less likely to participate in the subsequent screening than invitees with negative results. This association was found in all age groups and for both sexes. Further studies are necessary to assess whether non-attendance is more pronounced in specific subgroups.