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Bowel cancer screening to be considered from age 25 for high risk group

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by Cancer Research UK | News

23 March 2009

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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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