Screening for bowel cancer

Bowel cancers begin as small wart-like growths or ulcers in the lining of the bowel and, while still small and curable, they usually bleed. In most cases, the amount of blood in the faeces is so small that it is invisible to the eye; it is, however, detectable by a simple laboratory test. Taking the specimen for the test is done by the individual in his or her home. The process is painless and safe but a little distasteful. Research over the past 20 years has shown conclusively that testing the faeces for invisible (occult) blood provides a reliable method to discover early bowel cancer. People who test positive need further tests but, usually, bowel cancers detected in this way are small enough to be curable by simple surgery.

There are several genes associated with cancer of the colon and rectum, which singly or in combination can double or even quadruple the chance of getting the disease. Regular screening for people over the age of 50 can reduce the rate of death of colorectal cancers by one third. If the tests were offered to the whole population, the costs would be substantial – one estimate has put the cost of each prevented death at about US$200,000. Against that must be set the considerable cost, both social and financial, of treating people with incurable bowel cancers.

Over the last 20 years, death rates from bowel cancer have dropped more in women than in men. Some scientists believe this could be partly due to estrogen found in oral contraceptives and hormone replacement therapy.

A 13-year study conducted among 46,551 Minnesota residents found that yearly screenings for blood in stools reduced the number of deaths from cancers of the colon and rectum by one-third. Many colorectal cancers were detected at an early and curable stage, before symptoms were apparent. The tests also detected many adenomatous polyps, lesions in the bowel considered precancerous. The findings suggest that 1 in 10 people who are not considered at high risk for colon cancer will have a positive stool test, and in this group will be 92% of the colon cancers. If all American over age 50 took the test every year, more than a quarter of a million lives would be saved over the next 13 years, based on 1993 incidence of death rates.

A project in the Fyn region of Denmark began in 1985 and involved 140,000 people. Some had regular screening tests every two years, while others acted as controls. Mortality from bowel cancer was cut by 18%. A similar project in Nottingham, England, enrolled 153,000 people and cut morality by 15%. However the number of lives saved was smaller than has been reported from America, where mortality has been cut by 30% or more. Part of the explanation is that many of the people who signed up for screening stopped having the test after a few years. In the Nottingham study, nearly two-thirds of te participants dropped out, while in Fyn the rate was about half of the total.