Best Tests November 2006
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FOB Screen for CRC fails to reduce overall mortality
Bandolier 149 assessed a Cochrane review of occult blood testing for colorectal cancer screening. The key messages within this assessment are outlined below
The death rate from colorectal cancer was about 1 in 100 people over the whole period, or 1 in 1250 per year. The trials showed colorectal cancer deaths were reduced with screening, though the absolute effect was small. Almost 10,000 people needed to be screened for one year to prevent a single colorectal cancer death. The death rate from all causes was one in four over the whole period, about one in forty per year. Neither analysis by patient nor by patient year showed any difference between the screened and the control population in terms of overall mortality.
There are risks to testing. Over 80% of positive tests were false; the tests were positive but patients did not have cancer. These patients had the stress of receiving a positive test, and underwent further examination, which is not entirely benign. In 10,000 people an estimated 60-280 would have at least one colonoscopy, with 2-4 perforations or haemorrhages. Some of these will be fatal.
So for occult blood screening for one year, the chance of avoiding dying from colon cancer is 1 in 1200, while the risk of a perforation or haemorrhage is 1 in 3000. The author concludes that maybe it is better and more productive to get people to eat more fibre, especially when we can be pretty sure that screening in practice is unlikely to be as thorough as screening in trials.