CANCER RESEARCH-funded scientists have discovered that a genetic marker can be used to identify relatives of bowel cancer patients who are much more likely to develop the disease than the general population. The research suggests that for these families with an unusually high risk, screening for bowel cancer might be needed from the age of 25, while for those without the marker it is safe to start screening later. The study is published today in the Journal of Clinical Oncology*.
Researchers at the Institute of Cancer Research looked at 2,941people with bowel cancer** to see whether they carried bowel cancer genetic risk markers, using a test for microsatellite instablility (MSI)***. This test establishes if the genetic self-repair system is damaged allowing cancer-causing genetic mistakes to happen. They also asked the patients if their first degree relatives – parents, siblings or children – had bowel cancer and at what age they were diagnosed.
They discovered that if the tumours of a bowel cancer patient were MSI-positive and they were diagnosed at a young age, then their first degree relatives were up to twenty times more likely to develop the disease before the age of 70 compared with the general population. Of the 2,941 patients on the study, 344 were found to be MSI-positive – 11.7 per cent. The risks for relatives of MSI-negative patients were modest.
The researchers hope that doctors can use these findings to better calculate the risks of bowel cancer for this high risk group, which is likely to affect one to five per cent per cent of bowel cancer families, and decide on appropriate screening. This will help them catch the disease early, when treatment is more likely to be successful. It may also help prevent the disease from developing in some patients if they can detect pre-cancerous polyps and remove them before they become cancerous.
Professor Richard Houlston, lead author of the study which was co-funded by Cancer Research UK and the Institute of Cancer Research, said: “Screening programmes can be better tailored to individuals if information on the number of additional first degree relatives with bowel cancer is used in conjunction with information on MSI status.
“We suggest from these results that screening from the age of 25, is recommended for first degree relatives of bowel cancer patients whose tumour is positive for this genetic marker – especially if there are one or more other members of the family with the disease.
“We also think that doctors can delay screening first degree relatives of patients who were diagnosed before the age of 45 and who are MSI-negative for this genetic risk marker.”
Scientists already knew that first degree relatives of bowel cancer patients have a two-fold increased risk compared with the general public before the age of 70.
But the researchers deduced that if bowel cancer patients were additionally found to be MSI-positive, the risk of relatives developing the disease before the age of 70 increased to around four-fold that of the general population.
Additionally if bowel cancer patients were diagnosed at a young age – below 45 – then the risk of their first degree relatives developing bowel cancer before the age of 70 was around six-fold that of the general population. Furthermore, if bowel cancer patients were diagnosed young and were also found to be MSI-positive, then the risk to close relatives of developing bowel cancer increased to about 20-fold.
Dr Lesley Walker, Cancer Research UK’s director of cancer information, said: “This important research provides an accurate way to plan screening for the early detection of bowel cancer in high-risk families.
“Bowel cancer is one of the UK’s most common cancers and although three quarters of cases are found in people over the age of 65, we know that people with a first degree relative with the disease are at higher than average risk. Anything which helps us to further assess the level of risk means we can target measures aimed at preventing the cancer or detecting it early to those with greatest need.”
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*Implications of familial colorectal cancer risk profiles and MSI status. Steven J Lubbe et al. Journal of Clinical Oncology 2009.
Each year more than 36,500 people are diagnosed with bowel cancer in the UK, that’s 100 people every day. In 2006 there were 15,957 deaths from colorectal cancer in the UK, comprising 10,119 from colon and 5,838 from rectal cancer Bowel cancer is the third most common cancer in the UK and the second greatest cause of cancer death in the UK.
Faults in genes can occur every time cells divide and DNA is replicated. The genes which correct these faults are called mismatch repair (MMR) genes. But mistakes can’t be corrected if there is a mutation in any one of these MMR genes.
If mistakes lie within genes that are vital for cell function, then cells will grow abnormally and form a tumour.Microsatellites are chromosome regions particularly prone to errors during replication. A normal mismatch repair system will correct these errors and retain the original DNA sequence. However, a faulty mismatch repair system will not correct these errors, and accumulate and produce many variations in a genetic sequence as cells replicate,mutate and divide.
This is termed “microsatellite instability” (MSI) and is a sign that the mismatch repair pathway is not functioning correctly.
In England, the NHS Bowel Cancer Screening Programme will be rolled out in all areas by the end of 2009. Men and women aged between 60 and 69 years old are sent a stool testing kit every 2 years. People aged 70 and over can request a kit. From 2010, people aged 70 to 75 will also be included in the screening programme.
The national bowel screening programme in Scotland started in June 2007 to be rolled out across the whole country over two years. Men and women aged between 50 and 74 years are sent a stool testing kit every 2 years.
In Wales the NHS plans to test people between the ages of 50 and 74 every two years. Men and women aged between 60 and 69 from October 2008 receive stool testing kits. The NHS hopes to have rolled the service out to everyone else in the target age group by 2015.
In Northern Ireland the NHS plans to start screening in 2009.
This research has been funded by Cancer Research UK, the ICR, CORE, the European Commission and St. George’s Hospital, London.
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The Institute of Cancer Research
The Institute of Cancer Research is Europe’s leading cancer research centre with expert scientists working on cutting edge research. In 2009, The Institute marks its 100 years of world leading research into cancer prevention, diagnosis and treatment.
Scientists at the ICR have identified more cancer related genes than any other organisation in world. These discoveries are allowing for scientists to develop new cancer treatments.