Identification of subjects at risk of proximal advanced neoplasia for colorectal cancer screening

Flexible sigmoidoscopy (FS) and colonoscopy are two commonly used screening tools for colorectal cancer (CRC), and FS mainly detects distal lesions. Colonoscopy resource is limited, yet there is no definite evidence on when flexible sigmoidoscopy is suitable as a screening alternative. This study evaluated the optimal cut-off score from a validated risk stratification system which best predicts proximal advanced neoplasia (PAN) by comparing the sensitivity, specificity and relative risk of PAN according to various cut-off scores. 5819 asymptomatic subjects aged between 50 and 70 years (average age 57.7 years, standard deviation (SD) 4.9) received colonoscopy between 2008 and 2014 in Hong Kong. Their prevalence of PAN was evaluated according to a prediction tool for colorectal neoplasia based on age, gender, smoking status, family history of CRC, body mass index (BMI) and diabetes (ranging from 0 to 6). One binary logistic regression model was performed with PAN as the outcome variable and the risk score as the variable tested for association. In multivariate regression analysis, risk score ⩾3 was associated with significantly higher risk of PAN (3.4-9.1%; AOR = 3.18-8.09, p < 0.001) when compared with those scoring 0. Risk scores 0-2 were associated with either insignificant or lower risks of PAN compared to the overall risk. Applying FS for screening those who scored 0-2 and colonoscopy for those who scored ⩾3 led to a very small proportion of PAN being missed (1.60%), whilst maintaining a high level of specificity (81.9%). Clinicians may use this scoring system to inform subjects and facilitate their choice between colonoscopy and FS.