People referred were aged either 40 years or over with a first-degree relative with bowel cancer, or 50 years or over with marked anxiety about bowel cancer. This distribution of adenomas suggests that screening programs cannot rely solely on flexible sigmoidoscopy. Colorectal cancer is the most common internal malignancy in Australia and the second most common cancer overall. 1 One in 18 men and one in 27 women will develop this cancer during their lifetime. As most colorectal cancers are diagnosed at an advanced stage after symptoms develop, significant improvements in colorectal cancer mortality depend on prevention and early diagnosis.
Most colorectal cancers develop from adenomatous polyps.
If adenomas can be identified and removed, the adenoma-carcinoma sequence is broken, and colorectal cancer may be prevented. As adenomas usually cause few, if any, symptoms, they can be detected only by searching for them in asymptomatic individuals. This combination is probably the most accepted method of screening for average-risk colorectal cancer. However, as adenomas and cancers may occur on the right side of the colon, and as not all of these bleed, they could be missed by this combination of tests. In 1991, some private endoscopy centres in Melbourne, Victoria, developed a Bowel Cancer Prevention Program.