Verne, Julia Elvira Caroline Wanda; (1993) Screening for colorectal neoplasia in primary care. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The belief that most colorectal cancers evolve from pre-malignant adenomas underlies the hypothesis that flexible sigmoidoscopy (FS) screening, by detecting a higher proportion of adenomas, could make a greater impact on mortality than Haemoccult (Hct). Forecast low compliance, shortage of endoscopists, high polyp prevalence and unacceptable risks have delayed prospective evaluation of the efficacy of FS screening. The data described in this thesis are the results of a pilot study to evaluate the feasibility of flexible sigmoidoscopy screening based in primary care, and to compare this with Hct screening whose properties are well documented. 3,744 subjects aged 50-75 years from one general practice were randomised to be offered screening by FS, Hct, or both tests (HFS). The FS examinations were performed by a general practitioner. Corrected response rate in the FS group (50.5%), was significantly higher than in the Hct (34.6%) or HFS (34.1%) groups. A telephone reminder increased compliance with FS to 61.8%. 1116 FS screening examinations were performed to a high technical standard without major complication. Although many screenees suffered short-lived side-effects, 97% were willing to undergo another examination. Cancer was detected in four screenees and polyps in almost 20%. However, selecting "high-risk" individuals for colonoscopy by histological criteria would reduce the proportion from 19.3% to 2.4%, but screenees with polyps would still need polypectomy with the attendant risks. Only, 0.8% screened by Haemoccult had positive results but, Hct missed one cancer and many adenomas found by FS. In conclusion, compliance, logistics and side-effects do not appear to be obstacles to further evaluation of FS screening. However, the high polyp prevalence detected by FS screening remains a significant management problem which will need to be addressed in future studies.

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