National screening for colorectal cancer is associated with stage shift to earlier diagnosis

Background: Australia's National Bowel Cancer Screening Program consists of an immunohistochemical faecal occult blood test, targeting adults aged 50-74. Existing literature supports the principle of early detection of colorectal cancer (CRC) via national screening, but little is known about the association between colonoscopy or polypectomy rates and CRC stage over time. The aim of this study is to identify the longitudinal change to colonoscopy and polypectomy rates, and any stage shift associated with this screening program. Methods: A retrospective data-linkage study was performed using the Australian national health database (Medicare) to obtain colonoscopy and polypectomy rates between 1998 and 2017. A second prospective database of CRC resection specimens was analysed for this period. The cohort was divided based on time intervals related to the National Bowel Cancer Screening Program: pre-commencement 1998-2006 (Period A), immediately post-commencement 2007-2011 (Period B), and subsequent years 2012-2017 (Period C). Linear regression was used to test relation between annualized predictor and response variables. Results: Annual colonoscopy rates doubled, and polypectomy rates tripled during the study (P < 0.001). Annual colonoscopy rate correlated to a lower T-stage (P = 0.038) and lower N-stage (P = 0.026), and there was a 7% increase in early CRC (stage I-II) in Period C (P < 0.001). Across the study period there was also a significant increase in right-sided tumours, and concurrent MMR deficiency and BRAF mutation. Conclusion: Polypectomy and colonoscopy rates increased after the introduction of the National Bowel Cancer screening program. There was a clinically significant shift to earlier CRC stage which manifested 5 years after its implementation.