A common genetic trigger for bowel cancer has been identified for the first time.
The rogue gene, as yet unnamed, lies in a small chromosomal region that has also been linked to breast and prostate cancer.Around half the general population are thought to carry the genetic variant, which increases the risk of developing bowel cancer by about 20 per cent.The chances of suffering the disease rise from one in 20 for people who do not carry a faulty copy of the gene to one in 16 for those who do.Around one in 10 cases of bowel cancer in the UK are linked to the genetic defect, accounting for around 3,500 of the 35,000 cases diagnosed each year.The disease is the third most common cancer after breast and lung, and it causes almost 16,100 cases each year.Four separate scientific teams chasing the genetic causes of bowel cancer reported similar findings today in two different journals.Several genes are already known to contribute to the risk of bowel cancer, but they are extremely rare. Only around one person in every 2,500 carries one of these genes, and they account for less than five per cent of cases diagnosed each year.Even with the addition of the new genetic variant, the increased risk is still too small to be useful for a screening test.But experts believe as more “low risk” variants are found, it may be possible to spot them in combination and design a test for patients at high risk of bowel cancer.The discovery is the latest to emerge from new techniques that involve scouring the whole human genetic code for mutations linked to cancer.In this case, scientists homed in on a tiny stretch of DNA on chromosome eight – one of the 22 paired bundles of DNA found in every cell which, together with the X and Y chromosomes, house the genes.Comparisons between populations of patients with bowel cancer and healthy people revealed that the gene’s hiding place lay in this region.One study, published online in the journal Nature Genetics, was led by Professor Malcolm Dunlop from the University of Edinburgh and examined DNA from a total of 16,000 individuals from Scotland, France and North America.Prof Dunlop said: “Understanding all the genes involved is a bit like putting together a jigsaw puzzle in the dark. First we have to feel around for the genes involved and only then will we be able to find out how they all fit together to contribute to increased risk. By identifying these genetic variants, we will be in a better position to understand how such changes can lead to cancer.”A second study was jointly led by Professor Ian Tomlinson from Cancer Research UK’s London Research Institute and Professor Richard Houlston from the Institute of Cancer Research in Surrey and London.They studied about the same number of patients and healthy people in England, and also reported their findings in Nature Genetics.Similar work involving thousands of Israeli Jews and Arabs was conducted over a 10-year period by Dr Stephen Gruber, from the University of Michigan Medical School in Ann Arbor, US, and colleagues.They compared the genetic make-up and family history of more than 1,800 bowel cancer patients with that of 1,900 matched healthy people. The research, published in the journal Cancer Biology and Therapy, showed that the genetic variation might account for 14 per cent of bowel cancer cases in Israel, where the disease is the leading cause of cancer deaths.A fourth group of researchers, led by Dr Christopher Haiman, confirmed that some chromosome eight variants previously linked to prostate cancer were also associated with bowel cancer. This study, which looked at 1,807 individuals with bowel cancer and 5,511 healthy controls, was also published in Nature Genetics.The teams used a technique which involved searching for distinct blocks of DNA called “tags” that act as signposts for genes. Certain tags were more common in bowel cancer patients than healthy patients.By making repeated searches the scientists whittled the DNA markers down to just one tag on chromosome eight known as 8q24.Harpal Kumar, chief executive of Cancer Research UK, said: “This is an extremely important discovery which will significantly improve our understanding of the biology of bowel cancer and what causes it. In the future we hope studies like this across a range of cancers will help people at increased risk of the developing the disease through the development of tailored screening and treatment programs.”(Source: Cancer Research UK : July 2007)