A woman looking down a microscope

Is the rise in bowel cancer incidence due to screening?

This week we’ve released new figures showing bowel cancer is on the rise.

Between 2006 and 2008, the number of bowel cancer cases increased by around 10 per cent among people in their 60s.

After 10 years of stable bowel cancer rates, you might think that this would start alarm bells ringing. Far from it. The most likely cause of this new trend isn’t binge drinking or unhealthy diets brought on by the global economic downturn.

Instead the increase is almost certainly down to the introduction of bowel screening.

And the new figures suggest that screening is doing exactly what it set out to do.

What is bowel screening?

Bowel screening in the UK uses the faecal occult blood test (FOBT). The test looks for hidden traces of blood in the stools which can be a warning sign of bowel cancer. By finding tiny amounts of blood that are too small to see, it can help pick up the disease in the earliest stages, when most people can be cured.

Screening can also pick up growths in the bowel which could go on to develop into cancer.

Since July 2006, men and women in their 60s in England have been offered bowel screening with FOBT. In Scotland the test was introduced the following year for people aged 50 -75. Bowel screening started in Wales and Northern Ireland soon after.

The English and Welsh programmes are now being extended to include people up to the age of 74.

Why does screening cause an increase in cancer rates?

Bowel screening with FOBT prevents deaths from bowel cancer by finding the disease at an early stage, before it has symptoms. Screening can also find growths in the bowel called polyps which can develop into bowel cancer.

Scientists have shown that, over time, testing populations with FOBT can lead to a significant reduction in deaths from bowel cancer of around 16per cent.

But this won’t happen straight away. Most cancer screening programmes tend to lead to an increase in cancer rates first as screening picks up cancers that ordinarily wouldn’t have caused symptoms, or been detected, for another few years.

We saw this trend after breast screening was introduced in 1988. The dramatic increase in breast cancer rates only lasted for a few years when breast cancers without symptoms were picked up by screening, and the newness of the screening programme meant plenty of later stage symptomatic cancers were still being found outside the screening programme as well.

After around four to seven years, the breast screening programme was fully up-and-running and working as intended. Many breast cancers were picked up before they had symptoms but, correspondingly, fewer cancers had the chance to develop into later stage symptomatic disease, so breast cancer rates returned to levels more similar to before screening (although they were still rising slightly due to other factors) .

We’ll have to wait to find out if the pattern will be the same for bowel cancer.

Does this prove that bowel screening is a success?

The main aim of bowel screening is to cut deaths from bowel cancer. It’s too early to know if the screening programme is achieving that yet.

But bowel screening seems to be picking up more cancer cases in the screening age group – and that’s encouraging. Next, it will be important to look at the stage that these cancers are diagnosed to get a better picture of how successful the screening programme is.

As with almost all screening programmes, bowel screening raises the possibility of overdiagnosis. This is where the screening programme picks up bowel cancers which may not have gone on to cause any problems during a person’s lifetime. We’ll only know for certain to what extent overdiagnosis is a problem for bowel screening by waiting to see what happens to bowel cancer rates over the next decade.

What next for bowel screening?

The government recently agreed to introduce a new bowel cancer screening test – Flexi-Scope – into the existing programme. Cancer Research UK scientists showed last year that, as well as potentially cutting deaths, this new test could also prevent bowel cancer developing in the first place – a major breakthrough in the fight against this disease.

We hope that following the introduction of Flexi-Scope we’ll start to see a sharp decline in bowel cancer rates, with fewer and fewer people affected by this disease.