Colorectal cancer is the third most frequently diagnosed cancer worldwide, accounting for more than 1 million cases and 600 000 deaths every year.1 Survival is strongly related to stage at diagnosis, with survival rates of 90% for localised cases.2 Three randomised controlled trials3 have shown that biennial screening with the faecal occult blood test, which detects early cases, reduces mortality by around 25% in users of the test, and many countries have introduced screening programmes based on this test.4
Screening can potentially prevent colorectal cancers, because most arise from adenomas: predominantly symptomless growths that develop in 20–30% of the population.5,6 Two-thirds of colorectal cancers and adenomas are located in the rectum and sigmoid colon, which can be examined by flexible sigmoidoscopy. We have shown that flexible sigmoidoscopy is well accepted, safe, and quick,7–9 and would therefore be a suitable method for population screening if evidence of a worthwhile benefit is shown.
We did a large randomised trial to examine the hypothesis that only one flexible sigmoidoscopy screen undertaken between ages 55 and 64 years is a cost- effective and acceptable method to reduce colorectal cancer incidence and mortality. Our hypothesis is based on observations suggesting that most people who develop a distal colon cancer will have developed an adenoma by 60 years of age,10 and that removal of adenomas by sigmoidoscopy provides long-term protection against the development of distal colorectal cancer.11 Results from several epidemiological studies lend support to this hypothesis.12–14 Baseline findings from the trial were published in 2002,7 and in this Article we report the results after a median of 11 years of follow-up.