Science - September 3, 2010

Obese Lynch syndrome patients more at risk for colon cancer

People with the hereditary Lynch syndrome have considerably more risk of developing colon cancer. Obese people with this ailment also have twice as much risk of developing benign tumours in the large intestines compared with Lynch patients with a normal body weight.

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Overweight women with Lynch syndrome do not have any heightened risk of getting these adenomas (benign tumours), which are often the early stages of colon cancer.  This is the contention of PhD student Akke Botma in an article published in the Journal of Clinical Oncology last week. 'For people with Lynch syndrome, the DNA repair system does not work well. This can lead to tumours', says Botma. 'For Lynch syndrome patients, the risk that colorectal cancer will develop before they reach 70 years of age is 20 to 70 percent, compared with 2.5 percent for people without this ailment.'
Overweight
Lifestyle has a big influence on our health and the occurrence of certain diseases. Overweight is a major risk factor and a matter of concern because it is increasing among the Dutch population; a little less than half of the people at about age fifty are too fat. Overweight increases, among others, the risk of developing colon cancer. However, it is not clear if this also influences the risk of developing hereditary colon cancer. Botma therefore monitored 500 Lynch syndrome patients for two years to see if they developed benign adenomas. For each patient, she calculated the Body Mass Index or BMI, which is the number of kilos of the body weight divided by the square of the height. A BMI between the 20 and 25 indicates a normal weight; one above 25 can indicate overweight.
High-risk fats
Eventually, it appeared that more than 10 percent of the persons developed such adenomas during the observation period. 'We saw overweight men having a distinct heightened risk, at least twice as high, of developing the early stages of colon cancer', Botma says. 'This increased risk was not found in overweight women.' Botma attributes this difference between the sexes to the difference in fat distribution in men and in women. 'Men have mostly belly fats, which are fats surrounding the organs', Botma explains. 'These are high-risk fats and form a bigger health risk than the female hip fats.'
Botma concludes that men with Lynch syndrome and also men without this inherited abnormality have, on the average, twice as much risk of developing colon cancer if they are overweight. 'The risk of developing colon cancer is already high for Lynch syndrome patients; a doubling of this risk would be very much worse for them than for normal people', says Botma in evaluating her results. 'Risk groups should bear this in mind.'

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