Colorectal cancer screening within colonoscopy capacity constraints: can FIT-based programmes save more lives by trading-off more sensitive test cut-offs against longer screening intervals?

Introduction: Colorectal cancer (CRC) prevention programmes using faecal immunochemical testing (FIT) as the primary screen typically rely on colonoscopy for secondary and surveillance testing. Colonoscopy capacity is an important constraint, limiting the number of primary tests offered. Many European programmes lack sufficient colonoscopy capacity to provide optimal screening intensity regarding screening age ranges, intervals and FIT cut-offs. It is currently unclear how to optimise programmes within colonoscopy capacity constraints. Design: The MISCAN-Colon microsimulation model was used to determine if more effective CRC screening programmes can be identified within existing colonoscopy capacity. The model assessed 525 strategies of varying screening intervals, age ranges and FIT cut-offs, including previously unevaluated 4 and 5 year screening intervals. These strategies were compared with policy decisions taken in Ireland to provide CRC screening within available colonoscopy capacity. Outcomes estimated net costs, quality-adjusted-life-years and required colonoscopy numbers. The optimal strategies within finite colonoscopy capacity constraints were identified. Results: Combining a reduced FIT cut-off of 10 micrograms Hb/g, an extended screening interval of 4 years and an age range of 60-72 years requires 6% fewer colonoscopies, reduces net costs by 23% while preventing 15% more CRC deaths and saving 16% more QALYs relative to current policy. Conclusion: Previously overlooked longer screening intervals may balance optimal cancer prevention with finite colonoscopy capacity constraints. Simple changes to screening configurations could save lives, reduce costs, and relieve colonoscopy capacity pressures. These findings are directly relevant to CRC screening programmes across Europe that employ FIT-based testing and face colonoscopy capacity constraints.