Stage-specific risk of colon and rectal cancer in patients presenting with rectal bleeding or change in bowel habit in primary care: A population-based cohort study

Introduction: Rectal bleeding and change in bowel habit are red-flag symptoms for colon and rectal cancer but how they relate to advanced stage disease is not adequately understood. Methods: We analysed primary care electronic health records data on patients aged 30-99 years. Using logistic regression, we first examined the risk of colon and rectal cancer within 12 months in patients presenting with change in bowel habit and rectal bleeding, and then the risk of advanced stage at diagnosis within cancer cases. We combined the results to estimate risk of advanced stage colon and rectal cancers at diagnosis. Results: For both symptoms and sexes, risk of cancer (overall and by stage) increased with increasing age. We illustrate the findings for persons at the highest age-specific observed risk (typically aged around 80). In men, change in bowel habit (CIBH) and rectal bleeding were associated with different risk of advanced stage colon and rectal cancers (e.g., for colon, CIBH = 2.7% (95% CI 2.2-3.1) and rectal bleeding = 1.7% (95% CI 1.4-2.0)), but without evidence of risk difference between the two symptoms for non-advanced disease. The opposite pattern was apparent in women, with both symptoms associated with similar risk of advanced disease, but different risk of non-advanced colon and rectal cancers (e.g., for colon, CIBH = 1.0% (95% CI 0.8-1.3) and rectal bleeding = 1.3% (95% CI 1.1-1.6)). Discussion: Change in bowel habit and rectal bleeding have different age-specific associations with advanced stage disease, which vary by sex. A substantial proportion of cases is diagnosed at non-advanced stage, supporting the need for prompt diagnostic assessment of patients who present with those symptoms, taking into account the age-specific nature of risks.