Bowel cancer 'could be fuelled by E coli stomach bug'
Two-thirds of the 21 samples taken from
bowel cancer patients contained the bug, compared to just one in five of
those taken from healthy people
14:12 GMT, 20 August 2012
One of Britain’s most common cancers could be fuelled by the E coli stomach bug, scientists believe.
The breakthrough raises the prospect of a vaccine against bowel cancer, which claims 16,000 lives a year and is the second most common form of the disease in women after breast cancer and the third most diagnosed in men.
The elderly, who are most at risk of the bowel cancer, could also be screened for the ‘sticky’ strain of E coli that makes a DNA-damaging poison.
Tests showed Ecoli bacteria to be much more common in bowel cancer patients than in healthy people
Although the idea that a bug is involved in cancer might seem strange, it is not unheard of, with a virus being to blame for most cases of cervical cancer and a bacterium strongly linked to stomach cancer.
Now, tests on mice and people, carried out in the UK and US, have pointed to E coli being a strong suspect in bowel cancer.
The concern surrounds a version that sticks well to the inside of the lower bowel, or colon. It also contains genes that make a poison which causes the type of damage to DNA usually seen in cancer.
Although we usually think of E coli as causing food poisoning, these strains had been thought to live in the bowel without causing any problems.
However, tests show them to be much more common in bowel cancer patients than in healthy people.
Two-thirds of the 21 samples taken from bowel cancer patients contained the bug, compared to just one in five of those taken from healthy people, the journal Science reports.
Experiments also showed that mice inoculated with the bug are at very high odds of developing bowel cancer – as long as the E coli carries the poison-making ‘pks’ genes.
Liverpool University’s Dr Barry Campbell, a co-author of the study, said: ‘The research suggests that Ecoli has a much wider involvement in the development of colon cancer than previously thought.
‘It is important to build on these findings to understand why this type of bacteria, containing the pks genes, is present in some people and not in others.’
Professor Jonathan Rhodes said: ‘The bottom line message is that there seems to be a strong association between a type of E coli and the development of colon cancer.
‘And given that this type of E coli is specifically able to damage DNA and inflict the sort of damage you get in a cancer, it is very likely it has a causative role, at least in some patients.’
The scientists, who collaborated with scientists from the University of North Carolina, aren’t sure why some people who have the bug go onto develop cancer and others don’t.
But factors such as genes and diet are probably important.
Professor Rhodes said: ‘The literature on colon cancer taken as a whole suggests that having the right genes, taking exercise, possibly taking an aspirin a day, limiting red meat and eating plenty of leafy green vegetables all have a protective effect.’
If the link is confirmed, it could lead to tests for the rogue form of E coli being included in bowel cancer screening for the elderly.
In the long-term, a vaccine that stops the bug from taking root is also possible, added the professor.
There is a precedent for this – the HPV vaccine which is given to teenage girls wards off infection by the human papilloma virus – the bug behind the majority of cases of cervical cancer.
Henry Scowcroft, of Cancer Research UK, said: ‘This is an intriguing study in mice suggesting that the bacteria in our gut may play a role in the development of bowel cancer.
‘This would make sense, as we know that being infected with bacteria called H pylori can increase the chances of developing stomach cancer.
‘But since this study only involved mice and is still at an early stage, it’s not yet clear whether E coli is actually linked to bowel cancer in humans at all, let alone whether this knowledge could be used to help improve things for patients or people at risk.’