Evaluation of Flexible Sigmoidoscopy Screening as an Adjunct to the National FOBT Screening Programme in Scotland

Guaiac faecal occult blood testing (gFOBT) consistently demonstrates reductions in deaths from colorectal cancer of around 16% and gFOBT screening is now routine in all four countries of the United Kingdom. However, gFOBT has significant limitations and is associated with a substantial interval cancer rate in the region of 50 %, indicating a severe deficiency in sensitivity for cancer. Additionally, as the majority of colorectal cancers arise from pre-existing adenomas, it is important for colorectal screening programmes to detect adenomas in order to reduce the incidence of the disease as well as the associated mortality. Although gFOBT does detect some adenomas, most randomised trials have not demonstrated a reduction in colorectal cancer incidence. Also, FOBT screening tends to under-detect cancers in women and it is relatively insensitive for rectal cancer when compared with colon cancer. Single flexible sigmoidoscopy (FS), between the ages of 55 and 65 years, has been shown to bring about a significant reduction in colorectal cancer mortality. In addition, and most importantly, after a period of four years a significant reduction in colorectal cancer incidence was observed. FS does not suffer from low specificity since false positives do not occur, and there is independent evidence that it is more sensitive than a single gFOBT. In addition, FS is ideally suited to detecting rectal cancers and adenomas, and it is unlikely that there would be a gender difference in the sensitivity. Single FS has not been compared with biennial FOBT and there is no information regarding the utility of FS in a population that has already been exposed to FOBT screening. It is hypothesised that offering a combination of gFOBT and FS would provide an enhanced screening algorithm that would be associated with better outcomes than gFOBT alone. In order to test this hypothesis a randomised evaluation pilot study of FS screening integrated into the current gFOBT Screening Programme, wil