13:42 29 April 2010 by Jessica Griggs
Epidemiologist Wendy Atkin from Imperial College London explains how a revolution in bowel cancer screening could drastically cut the death rate.
How does this screening work?
It involves examining the lower third of the bowel, where more than half of bowel cancers are located. A nurse looks inside the bowel using a flexible instrument with a camera on the end called a sigmoidoscope, or Flexi-Scope. This transmits an image onto a TV monitor so we can examine the surface of the bowel wall for polyps – clusters of cells that can become cancerous over the course of someone's life. These can be removed by threading a kind of lasso down the Flexi-Scope and pinching them off. It's a painless procedure and can be done in about 5 minutes. Removing these polyps through the Flexi-Scope prevents them from turning into cancers.
How does this compare with current screening?
We [currently] use a faecal occult blood test (FOBT), which involves looking for traces of blood in your stool at home. This could be a sign of very early cancer. If it is positive, you have a colonoscopy to find the source of the bleeding. A colonoscope is like a longer version of the Flexi-Scope but it can examine all around the bowel.
The big difference between the FOBT and the Flexi-Scope is that the stool test detects the early cancer but doesn't find the polyps, so it can't prevent the disease and cut the number of new cases of bowel cancer.
How do you know how effective the test is?
It is already used in the US, but in the UK we've just completed the first randomised trial with 170,000 people aged 54 to 65 – the age at which most people prone to polyps will have developed them.
Having the test reduced the risk of getting the disease throughout the whole bowel by a third and the risk of dying from bowel cancer by more than 40 per cent, compared with 25 per cent for the FOBT.
And one of the best things is that you only need to take the Flexi-Scope test once?
That's what the result show so far – after 11 years there was no sign of the polyps recurring. We will follow the trial group for the rest of their lives to see whether one test really is enough.
Back in 1994, we came up with a theory that most bowel cancers arise from polyps, and most polyps in the lower bowel develop by the time you're 60. So if you examine the bowel just before someone is 60, then you should be able to classify them as having polyps, and remove them – or not having polyps, and therefore not destined to get them because they would have already done so.
Would this screening replace FOBT? And what about genetic cancer?
You would have the Flexi-Scope exam in your 50s and follow that up with the FOBT in your 60s, thereby ensuring you were screened for cancer in both upper and lower bowel.
Someone with a genetic risk is likely to be at increased risk of developing polyps. But if there is a strong family history, suggesting genetic risk, it might be better to have regular colonoscopy.
Will the test be accepted as part of the UK's National Health Service screening programme?
Having proven that it works, it's now down to the economic analysis but we have already worked out that for every person screened, the NHS saves £28 on potential treatment costs.
Journal reference: The Lancet, DOI: 10.1016/s0140-6736(10)60551-x (in press)
