Reviewed 16 Nov. 2005

Incidence and mortality rates for colorectal cancer in Canada are among the highest in the world, although they are lower in B.C. than in central and eastern Canada. Incidence rates have shown a modest decline among women since the mid- 1980's whereas they have remained unchanged among men over the last 20 years. The reason for the gender difference in incidence is unclear. Mortality rates have shown a steady decline in both sexes.

Diet is an important factor in the causation of this disease. Risk increases with higher dietary fat and meat consumption, and lower fibre, fruit and vegetable consumption. A positive family history, or history of specific inherited disorders (e.g. Familial adenomatous polyposis) increases risk. Prior inflammatory bowel disease also increases subsequent risk of colon cancer. A number of well-conducted studies have shown a higher risk of colon cancer in those with low physical activity levels. Alcohol intake appears to increase risk of rectal cancer. The presence of long-term, non-functioning rectal tissue (for instance, after permanent diverting colostomy or a colectomy (but not proctectomy) with ileostomy creation) is an independent risk factor for development of rectal cancer (within the remaining rectum) or carcinoma of the stoma, usually many years following the initial surgery. This possibility should be borne in mind in patients with intact, but not "connected" rectum who present with bleeding. Other possible risk factors include obesity in both sexes, and low parity in females. Non-steroidal anti-inflammatory drug usage appears likely to reduce risk.

Prevention

Lifestyle modification through improved diet and higher levels of physical exercise offers the best opportunity to reduce colorectal cancer incidence. Screening by fecal occult blood testing has been shown to reduce colorectal cancer mortality by 25 – 45%. This screening test also potentially allows for the primary prevention of colorectal cancer by identifying adenomatous polyps. Preventive and screening strategies for patients with adenomatous polyposis coli and inflammatory bowel disease are discussed below.

References:

1. Schottenfeld D, Winawer SJ. Cancers of the large intestine in Schottenfeld D, Fraumeni JF Jr. (Eds) Cancer Epidemiology and Prevention 2^nd Ed. 1996. Oxford University Press, Oxford. Pp 813-840.
2. Thompson-Fawcett MW, Marcus V, Redston M, Cohen Z, McLeod RS, "Dysplasia risk in long-term ileal pouches and pouches with chronic pouchitis", Gastroenterology 2001; 121: 275-81.