Impact of colorectal cancer in the UK

Colorectal (large bowel) cancer is the second commonest cause of cancer related death in the western world and there are more than 30 000 new cases per annum in the UK with an average five year survival of 40%.1-3 Symptoms of colorectal cancer include change in bowel habit, rectal bleeding, anaemia, and abdominal pain but patients with colorectal cancer often have no symptoms until the cancer is advanced. Ninety per cent of cases are currently not diagnosed until the cancer has penetrated through the bowel wall or spread to lymph nodes or elsewhere (Dukes' stages B–D).4 Such cases have a much worse chance of surviving five years (64%, 38%, and 3%, respectively for Dukes' B, C, and D) than patients who present with cancer confined to the bowel wall (Dukes' A) who have approximately 83% chance of surviving five years. Because so many patients with colorectal cancer do not develop symptoms until their cancer is advanced, detection of a greater proportion of cases at an earlier stage can only be achieved by screening of asymptomatic individuals.

It is thought that 70–90% of cases of colorectal cancer arise from premalignant (adenomatous) polyps.5 They often have a stalk which consists of healthy tissue and allows them to be removed simply and completely by endoscopic snaring. This polyp to cancer sequence adds a strong intellectual argument in support of screening for colon cancer as it provides an opportunity not only to achieve early diagnosis (for example of Dukes' stage A carcinomas) but actually to prevent cancer development by removal of premalignant polyps.

There is evidence that approximately 10% of colorectal cancers are due to genetic causes but that about 90% of the cause is accounted for by environmental factors, particularly diet.6 The dietary factors involved are not fully understood …