Smoking may increase colorectal cancer risk
SAN FRANCISCO, Apr 05 (Reuters Health) -- If the threat of lung cancer isn't enough to make you kick the habit, results of a new study suggest that smokers are at higher risk of developing intestinal polyps, which may increase colorectal cancer risk.
However, the good news is that this risk can be markedly reduced by stopping smoking, according to investigators from the National Cancer Institute.
While past studies have found that smokers are more likely to develop intestinal polyps, the new study found that polyps in smokers are more aggressive -- that is, more likely to develop into cancer -- than polyps in nonsmokers. Intestinal polyps are dangerous because they may progress to cancer.
The new findings were presented by Dr. Richard B. Hayes on Tuesday at the 91st annual meeting of the American Association for Cancer Research here.
Hayes and colleagues looked at a total of 27,924 people who filled out a risk factor questionnaire and underwent screening with sigmoidoscopy, an examination of the lower colon with a lighted instrument.
Those people with one or more polyps were usually referred for colonoscopy, an examination of the entire colon. Overall, 110 people had colorectal cancer, 1,954 people had intestinal polyps and of those, 1,550 had polyps in the descending colon, where the majority of colon cancers develop.
The investigators found that patients with colorectal cancer were more likely to be smokers, as were those who had polyps in the descending colon. What's more, smokers appeared to have more aggressive polyps, based on the size and cellular changes of the growth.
``We found that duration of tobacco use was also an important risk factor,'' Hayes said. ``The longer people used cigarettes, the greater the risk was.'' The amount of tobacco used also increased the risk.
However, ``quitting the use of cigarettes had a profound impact on the subsequent risks for all of these conditions -- for the adenomas (intestinal polyps) and the cancers.''
While the risk dropped off over time after smoking cessation, ``this effect was more rapid for the smaller adenomas,'' he added. ``There continued to be an excess risk for larger adenomas and cancer, which is consistent with the notion that these cancers take a long time to develop.''
This study is ``particularly striking and important in that it implicates tobacco in yet another one of the big four diseases,'' Dr. Louis M. Weiner of the Fox Chase Cancer Center in Philadelphia, Pennsylvania, said. Colorectal, lung, breast, and prostate cancer are the four most common cancers in the US.
``We have iron-clad evidence that lung cancers are associated with tobacco use,'' Weiner continued. ``And while these current data are admittedly preliminary, if they hold up under further scrutiny, this will imply tobacco use as another very important environment factor that interacts with the genetic environment of the individual to enhance the likelihood of developing this terrible cancer.''