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Background: Earlier diagnosis of colorectal cancer could help improve survival so better tools are needed to help this. Aim: To derive and validate an algorithmto quantify the absolute risk of colorectal cancer in patients in primary care with and without symptoms. Design and setting: Cohort study using data from 375 UK QResearch® general practices for development and 189 for validation. Method: Included patients were aged 30-84 years, free at baseline froma diagnosis of colorectal cancer and without rectal bleeding, abdominal pain, appetite loss, or weight loss in the previous 12months. The primary outcome was incident diagnosis of colorectal cancer recorded in the next 2 years. Risk factors examined were age, bodymass index, smoking status, alcohol status, deprivation, diabetes, inflammatory bowel disease, family history of gastrointestinal cancer, gastrointestinal polyp, history of another cancer, rectal bleeding, abdominal pain, abdominal distension, appetite loss, weight loss, diarrhoea, constipation, change of bowel habit, tiredness, and anaemia. Cox proportional hazardsmodels were used to develop separate risk equations inmales and females. Measures of calibration and discrimination assessed performance in the validation cohort. Results: There were 4798 incident cases of colorectal cancer from4.1million person-years in the derivation cohort. Independent predictors inmales and females included family history of gastrointestinal cancer, anaemia, rectal bleeding, abdominal pain, appetite loss, and weight loss. Alcohol consumption and recent change in bowel habit were also predictors inmales. On validation, the algorithms explained 65%of the variation in females and 67%inmales. The receiver operating curve statistics were 0.89 (females) and 0.91 (males). The D statistic was 2.8 (females) and 2.9 (males). The 10%of patients with the highest predicted risks contained 71%of all colorectal cancers diagnosed over the next 2 years Conclusion: The algorithmhas good discrimination and calibration and could potentially be used to help identify those at highest risk of current colorectal cancer, to facilitate early referral and investigation. ©British Journal of General Practice.

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British Journal of General Practice

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