PS 1-35
THE IMPACT OF TIME TO DIAGNOSTIC ASSESSMENT ON SCREENING EFFICACY
Method: We used four disease-specific models to simulate annual screening with a fecal immunochemical test (FIT) from age 50 to 75 years for colorectal cancer, biennial mammography screening from age 50 to 75 years for breast cancer, and triennial Papanicolaou testing from age 21 to 65 years for cervical cancer. We compared screening regimens with time to follow-up (T2FU) after a positive result set to 0, 3, 6, 9 or 12 months. We evaluated the clinical impact of T2FU based on the stage distribution at diagnosis, the proportion of cancers that were clinically detected, and the fraction of cancers prevented and life years gained (LYG) relative to no screening.
Results: Screening results in a more favorable stage distribution, with cancers detected earlier in screened versus unscreened cohorts. This benefit declined with longer T2FU, especially for breast and colorectal cancers. For breast cancer, screening increases cancer incidence while for cervical and colorectal cancer, screening prevents cancer through removal of precursor lesions, decreasing cancer incidence. The maximum benefit of screening, in terms of LYG per 100,000, is achieved when positive tests are followed up immediately. With a 3-month T2FU, the effectiveness of screening was reduced, based on the percent of this maximum LYG achieved (breast: 82.1%, cervical: 99.2%, colorectal: 96.5% to 97.1%); 12-month T2FU resulted in further reductions in screening effectiveness (breast: 38.1%, cervical: 97%, colorectal: 89.7% to 88.2%).
Conclusion: Screening is highly effective across all cancers, even when follow-up of positive screening tests is not immediate. However, increasing the follow-up interval can lead to meaningful reductions in overall screening effectiveness.