Scientists find bowel cancer genes that triple risk
Cancer Research UK funded scientists have identified two common genetic variants that could triple a person's risk of getting bowel cancer. Their findings are published in Nature Genetics1 today (Sunday).
Earlier this year, Cancer Research UK funded scientists found the first genetic region commonly associated with bowel cancer risk when they undertook a search of the human genome. The paper published today and another paper published last month2 identify two areas near specific genes that strongly influence bowel cancer risk.
The researchers estimate that up to a third of all bowel cancers may be associated with these newly identified, high-risk variants of the genes - about 12,000 cases per year in the UK. The increased risk of bowel cancer when these two genes are present is small, but if both these and two other high-risk genetic variants identified earlier this year are present, a person can have a two to three fold increased risk of bowel cancer.
In a previous investigation, the researchers located a genetic region responsible for Hereditary Mixed Polyposis Syndrome (HMPS) - a condition that increases bowel cancer risk in Ashkenazi Jews3. In this study, the search was narrowed down to try to find the specific genes responsible for HMPS by analysing the genomes of nearly 15,000 people, including nearly 8,000 bowel cancer cases.
The scientists didn't find any genes directly responsible for HMPS but instead found that the HMPS region contained other genes that increase bowel cancer risk in the general UK population.
The study was jointly led by Professor Ian Tomlinson from the London Research Institute and Professor Richard Houlston from The Institute of Cancer Research.
Professor Ian Tomlinson, joint lead researcher based at Cancer Research UK's London Research Institute said: "We're delighted to have taken our research forward to pin down genes that influence a person's risk of developing bowel cancer. Increasing our understanding of genes like this may make it possible for scientists to eventually develop ways of stopping many people at increased risk of bowel cancer from developing the disease altogether.
"Finding out that a region we thought was only relevant to bowel cancer risk in Ashkenazi Jews was also related to risk in the wider UK population is very important. This could help us understand how different variants of the same gene affect risk and how genes interact to increase overall risk."
Professor Richard Houlston, joint lead researcher based at The Institute of Cancer Research, said: "This is an exciting development in our understanding of how bowel cancer develops, a disease which kills more than 16,000 people in the UK each year. By pinpointing more genes which increase an individual's risk of bowel cancer we ultimately hope to improve diagnosis and treatment of this cancer."
The increased risk incurred as a result of these individual genetic faults is relatively small so genetic testing for these alone would not be worthwhile. But it may be possible to design a test for a combination of genes as more 'low risk' variants are found. Identifying people who have an increased risk of developing bowel cancer will improve prevention, diagnosis and treatment of the disease in the future.
Dr Lesley Walker, Cancer Research UK's director of cancer information, said: "Cancer Research UK is launching a series of genome wide studies, including searches for genes that influence lung and ovarian cancer risk. Discoveries like this will improve our understanding of cancer and help us to develop targeted screening and treatment for people at increased risk of the disease."
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Notes to Editor
- "Common genetic variants at the HMPS/CRAC1 locus on chromosome 15q13.3 influence the risk of colorectal cancer in the UK." E Jaeger, et al. (2007) Nature Genetics.
- "A genome-wide association study shows that common alleles of SMAD7 influence colorectal cancer risk." P Broderick, et al. (2007) Nature Genetics.
- Jewish population of central and Eastern European descent.
The technology used in these studies was provided by Illumina.
The researchers were based at Cancer Research UK's London Research Institute, London, Institute of Cancer Research, Sutton, Bart's and the London Medical School, Queen Mary College, KBW/Center for Biomedicine, Switzerland, St Mary's Hospital, Manchester, Birmingham Women's Hospital, Oxford University, University of Birmingham, University of Edinburgh, Institute of Cancer Research, London, London School of Hygiene and Tropical Medicine, Family Cancer Clinic and Imperial College, St Mark's Hospital, Harrow.
Every year in the UK, around 36,000 people are diagnosed with bowel cancer. It is the third most common cancer after breast and lung and the disease causes almost 16,100 deaths in the UK every year. Around two-thirds of cases are in the large bowel (colon) and the remaining third are in the back passage (rectum). The occurrence of bowel cancer is strongly related to age, with over 80 per cent of cases arising in people who are 60 years of older.
One factor that can increase risk of developing bowel cancer is an inherited faulty gene (genetic mutation). An inherited genetic mutation may mean that several people on the same side of a family develop bowel cancer. This is called a 'strong family history'. It can also mean there are one or more relatives diagnosed at a particularly young age. There are a number of known genetic conditions linked to bowel cancer, including familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC).
People who are concerned they may have a strong family risk should talk to their GP. The doctor may refer them to a genetics clinic for specialist advice about their risk, screening and the availability of genetic testing.
The tendency of cancers to aggregate in families cannot be wholly explained by rare, high-risk, inherited mutations. A substantial proportion of such cancers are thought to be attributable to the combined effects of multiple, common gene variants, known as polymorphisms, each of which is associated with a small increase in cancer risk. The search for these polymorphisms is being facilitated by the availability of the human genome sequence and the development of high-throughput single nucleotide polymorphism (SNP) array technology, as used in this study.
Bowel cancer screening
Screening means looking for early signs of a particular disease in 'healthy' people who don't have symptoms. Results from large scale Government pilot studies published in 2003 suggested that a national bowel screening of the normal population would help save lives. The Government is now phasing in a national screening programme across the country.
In England, men and women aged between 60-69 years old are being offered a test every two years. The screening method used is called faecal occult blood testing (FOB). Faecal occult blood testing means looking for hidden (occult) blood in your stool (faeces). People can do the test themselves at home.
For more information about bowel cancer or screening visit our patient information website CancerHelp UK.
About The Institute of Cancer Research
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The Institute is a charity that relies on voluntary income. The Institute is one of the world's most cost-effective major cancer research organisations with over 90p in every £ directly supporting research.
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