Impact of the Australian National Bowel Cancer Screening Program on Stage at Diagnosis and Stage-Specific Survival in Colorectal Cancer.

AIM: The Australian National Bowel Cancer Screening Program began in 2006, offering free faecal occult blood testing every 2 years to Australians aged 50-75 years. We hypothesised a difference in overall survival between screen-detected and non-screen-detected colorectal cancer in an Australian cohort, for each stage I-III. METHODOLOGY: A retrospective cohort study of patients with stage I-III colorectal cancer from 2010 to 2024 was conducted using a prospectively maintained institutional database. Overall survival (OS) was calculated from the date of diagnosis. Kaplan-Meier analysis and log-rank testing were used to compare survival between screen-detected and non-screen-detected cancers, stratified by stage. RESULTS: A total of 881 colorectal cancer episodes were included, of which 254 (28.8%) were screen-detected. The proportion of screen-detected cancers increased significantly over time (Cochran-Armitage trend test, p < 0.001). Screen-detected cancers were diagnosed at an earlier stage, with a significantly higher proportion of stage I disease than non-screen-detected cancers (38.6% vs. 18.0%, p < 0.001). Five-year OS for stage I disease was 93.9% in the screen-detected group and 90.8% in the non-screen-detected group (HR 0.62, 95% CI 0.30-1.28; p = 0.19). Corresponding five-year OS for stage II disease was 91.3% and 85.6%, respectively (HR 0.70, 95% CI 0.33-1.48; p = 0.35). In stage III disease, 81.5% vs. 68.9%, respectively (HR 0.56, 95% CI 0.34-0.92; p = 0.02). CONCLUSIONS: Screen-detected colorectal cancer is associated with earlier stage at diagnosis and improved survival in stage III disease. These findings support the role of screening in earlier diagnosis and improved oncological outcomes.