Oral Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2024

Risk Factors of Colorectal Cancer after a Colonoscopy: A Retrospective Cohort Study of Australian Patients Aged 75 and Older (#21)

Molla M Wassie 1 , Geraldine Laven-Law 1 , Jean M Winter 1 , Norma Bulamu 1 , Liz Buckley 1 , Joshua Trigg 1 , Peter Bampton 2 , Charles Cock 1 3 , Erin Symonds 1 3
  1. Flinders Health and Medical Research Institute, Flinders University, Bedford Park, SA, Australia
  2. SA Group of Specialists , Adelaide , SA, Australia
  3. Department of Gastroenterology and Hepatology, Flinders Medical Centre , Bedford Park, SA, Australia

Aims: Colorectal cancer (CRC) risk increases with age and can be prevented through ongoing surveillance colonoscopy. However, colonoscopy is generally not recommended beyond age 75y. This study aimed to determine predictors of post-colonoscopy CRC (PCCRC) in people aged ≥75y.

Methods: We conducted a retrospective observational cohort study on individuals aged ≥75y at above-average risk of CRC (due to a prior history of colorectal neoplasia and/or a significant family history of CRC). All individuals were enrolled in a South Australian CRC surveillance program (SCOOP) and undergoing surveillance colonoscopy at guideline-recommended intervals until age 75y. Demographics, family history of CRC, colonoscopy and prior faecal immunochemical test (FIT) results before turning 75y were extracted from clinical records. CRC was identified through data linkage with the South Australian Cancer Registry. Predictors of PCCRC were identified using Cox proportional hazards regression.

Results: A total of 126 PCCRC cases were diagnosed in 3,842 individuals aged ≥75y (54.9% male). The median follow-up time from last colonoscopy was 7.9 years per person (interquartile range 3.1-13.2). Older age (hazard ratio [HR] 2.6, 95% confidence interval [CI] 1.6-4.1, for those aged 80-85y; HR 3.3, 95% CI 1.7-6.4, for those aged above 85y, previous resection of advanced neoplasia (including high-grade dysplasia, size ≥10mm, villous component, or ≥3 tubular adenomas) (HR 1.8, 95% CI 1.2-3.3), immediately  prior incomplete colonoscopy (HR 3.0, 95% CI 1.7-5.2) and greater number of total prior colonoscopies (HR 1.2, 95% CI 1.1-1.4), were each associated with increased risk of developing PCCRC. Risk for PCCRC was reduced for those with greater number of FIT completion (HR 0.8, 95% CI 0.7-0.9).

Conclusion: PCCRC presents a clinical challenge in people aged ≥75 years. Risk factors for PCCRC, such as previous colonoscopy outcomes (e.g., advanced neoplasia), can help guide the development of future non-invasive surveillance strategies in this increased risk older population.