Primary and secondary prevention in colorectal cancer.

Colorectal cancer is an important public health problem: there are nearly one million cases of colorectal cancer diagnosed worldwide each year and half a million deaths. The geographic distribution of colorectal cancer follows the division between westernized versus developing countries, The highest rates are in North America, Australia and Europe. Rates in Africa and Asia are low, but are increasing in countries adopting western-style dietary habits. Given that the majority of cancers occur in older people, and with the ageing of the population in mind, this observation adds impetus to investigating prevention strategies to avoid some of this increase. High vegetable and fruit consumption has been associated with decreased risk of colorectal cancer in numerous observational studies, while high fibre intake seems to have a similar effect. Promising data have been obtained for aspirin and other non-steroidal anti-inflammatory drugs, and dietary calcium. A physically active lifestyle and maintenance of normal body weight are behavioural tools for prevention of colorectal cancer. Faecal occult blood testing has been shown to be effective in the prevention of about 20% of deaths from colorectal cancer, but few population-based screening programs have been initiated. Sigmoidoscopy and colonoscopy are potentially effective screening modalities; however, no randomized trial data have yet been reported. Overall, primary and secondary prevention, chemoprevention and screening research and implementation of these prevention strategies are priorities for reduction of colorectal cancer incidence and mortality.