Poster Session II - A264 HIGH RISK OF COLORECTAL CANCER AFTER COLONIC HIGH-GRADE DYSPLASIA IN PATIENTS WITH INFLAMMATORY BOWEL DISEASE

Abstract Background There are limited data on colorectal cancer (CRC) risk after a previous diagnosis of high-grade dysplasia (HGD) in inflammatory bowel disease (IBD). Aims To determine the long-term CRC risk and cumulative incidence of metachronous colorectal neoplasia (CRN) after a first diagnosis of HGD in IBD, and to assess utilization of HGD treatment strategies over the past three decades. Methods In this nationwide retrospective cohort study, data from patients with colonic IBD and a diagnosis of HGD between 1991 and 2021 were extracted from the Dutch nationwide pathology databank (PALGA). The primary outcome was the cumulative incidence of metachronous CRC. Kaplan-Meier curves were used to show proctocolectomy-free survival per decade. Results CRC was diagnosed in 348 of 1,220 patients with HGD (28.5%). Of these, 204 patients (16.7%) were diagnosed with CRC within 6 months after the first HGD diagnosis and were considered synchronous cases. Metachronous CRC was diagnosed in 144 of 1,016 patients (14.2%) after a median of 3.6 years. The 1-, 5-, and 10-year cumulative incidences of metachronous CRC after HGD were 2.9%, 10.0%, and 15.9%, respectively. The 1-, 5-, and 10-year cumulative incidences of metachronous CRN were 18.3%, 54.0%, and 75.2%, respectively. We observed a decrease in proctocolectomy-free survival after HGD over time (Table 1). Conclusions The combined risk of synchronous and metachronous CRC after a diagnosis of HGD is almost 30%. The advantages of colon-sparing treatment should be balanced with the higher risk of metachronous CRC and the subsequent need for stringent endoscopic surveillance. Funding Agencies None