Advanced serrated polyps as target of screening: detection rate and positive predictive value within a fecal immunochemical test based colorectal cancer screening population

Aims Advanced serrated polyps (ASPs) have a comparable risk as advanced adenomas (AAs) to progress into colorectal cancer (CRC). The yield of most CRC screening programs, however, is based on AAs and CRC only. We assessed the ASP detection rate, and increase in positive predictive value (PPV) including ASPs in the yield of a FIT-based screening program. Methods We analysed findings of follow-up colonoscopies of FIT-positive screenees in the Dutch CRC screening program from 2014 until 2020. Data was retrieved from the national screening and pathology database. ASP was defined as any serrated polyp ≥10mm, sessile serrated lesion with dysplasia or traditional serrated adenoma. ASP detection rate was defined as the proportion of colonoscopies with ≥1 ASP. PPV was defined as proportion of persons with a CRC or AA. The updated PPV definition included CRC, AA and/or ASPs. Results In total, 322,882 colonoscopies were included in the analyses. Overall detection rate of ASPs was 5.9%. ASPs were more often detected in females than males (6.3% vs 5.6%, p<0.001). ASP detection rates in individuals aged 55-59, 60-64, 65-69 and 70+ were 5.2%; 6.1%; 6.1%; 5.9% (p<0.001), respectively. The PPV for CRC and AA was 41.1% and increased to 43.8% when including ASP. The PPV increase was larger in females than in males (3.2% vs 2.4%). <u>Conclusion</u> A proportion of 5.9% FIT-positive screenees had ASPs, but half of these were detected in combination with CRC or AA. Therefore, including ASPs results in a small increase in the yield of FIT-based screening.