Adenoma characteristics in the English Bowel Cancer Screening Programme

Aim: The English Bowel Cancer Screening Programme detects colorectal cancers and premalignant polyps in a faecal occult blood test-positive population. The aim of this work is to describe the detection rates and characteristics of adenomas within the programme, identify predictive factors influencing the presence or absence of carcinoma within adenomas and identify the factors predicting the presence of advanced colonic neoplasia in different colon segments. Method: The Bowel Cancer Screening System was retrospectively searched for polyps detected during colonoscopies between June 2006 and June 2012, at which time a guaiac test was being used. Data on size, location and histological features were collected, and described. Univariate and multivariate analyses were used to determine the significant factors influencing the development of carcinoma within an adenoma. Results: A total of 229 419 polyps were identified; after exclusions 136 973 adenomas from 58 334 patients were evaluated. Over half were in the rectum or sigmoid colon. Subcentimetre adenomas accounted for 69.8% of the total. The proportion of adenomas containing advanced histological features increased with increasing adenoma size up to 35 mm, then plateaued. A focus of carcinoma was found in 2282 (1.7%) adenomas, of which 95.6% were located distally. Carcinoma was identified even in diminutive adenomas (0.1%). The proportion of adenomas containing cancer was significantly higher in women than men (2.0% vs. 1.5%, p < 0.001). Conclusion: This national, prospectively captured dataset adds robust information about histological features of adenomas that convey an increased risk for colorectal cancer, and identifies caecal adenomas, high-grade dysplasia, increasing adenoma size, distal location and female sex as independent risk factors associated with carcinoma.