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Figure  . Gllomas and chemotherapy

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Cigarette smoking may be responsible for a significant percentage of colorectal cancers, according to new evidence uncovered by American Cancer Society (ACS) epidem-iologists and published in the Journal of the National Cancer Institute (2000;92:1888-1896).

The researchers found colorectal cancer death rates were lowest among people who had never smoked, intermediate among ex-smokers, and highest among current smokers. The risks of dying of the disease increased with the number of cigarettes smoked daily and the number of years of smoking. Also, the younger the person was when he or she began smoking, the higher the risk.

The ACS team studied data on 312,332 men and 469,019 women collected as part of the Society's Cancer Prevention Study II. Along with smoking, they took into account other colorectal cancer risk factors, such as a diet low in fruits and vegetables and high in fat, getting too little exercise, and being overweight.

The risk increased when a person had smoked for 20 years, but decreased with each year after quitting smoking. “While it's best not to start at all, quitting early can still lower the colorectal cancer death rate,” says Ann Chao, PhD, lead author and a research epidemiologist with the ACS.

While it's best not to start at all, quitting early can still lower the colorectal cancer death rate.

The study also found that women who smoked were more than 40% more likely to die from colorectal cancer than women who never had smoked, and male smokers had more than a 30% increase in risk of dying compared with men who never had smoked.

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Cigarette smoking has previously been linked to cancers of the lung, mouth, pharnyx, larynx, esophagus, pancreas, kidney, and bladder. Chao et al say the relationship between smoking and colorectal cancer means that getting early detection tests is especially important for current and former smokers. “Findings from this and other large studies suggest that colorectal cancer should be reconsidered for classification as a smoking-related cancer,” she says.