NEW YORK (Reuters Health) - Women who smoke cigarettes for 30 years or more appear to be at increased risk for rectal cancer, according to a recent report. Such long-term smoking, however, does not appear to increase the risk of colon cancer.

While the link between smoking and development of colorectal adenomas is well established, the association between smoking and colorectal cancer has not been clear. Study author Dr. Paul D. Terry, from the Albert Einstein College of Medicine in New York, and colleagues hypothesized that this apparent paradox may be explained if cancer develops only after some 35 years from smoking commencement. In the current study, the link between smoking and colorectal cancer was evaluated in 89,835 women who participated in the Canadian National Breast Screening Study. At the time of recruitment, between 1980 and 1985, the women were 40 to 59 years of age. During an average followup period of 10.6 years, 363 women were diagnosed with colon cancer and 164 with rectal cancer, the authors note in the May 20th issue of the International Journal of Cancer. Women who had smoked for at least 40 years' duration were 3.14 times more likely to develop rectal cancer than never smokers. In addition, women who had started smoking at least 30 years prior to evaluation were at increased risk for rectal cancer. In contrast, smoking, even of long duration, was not identified as a risk factor for colon cancer. "The results of the present study support the hypothesis that tobacco smoking is an initiator, rather than a promoter, of rectal cancer," the author state. The reason for a link between smoking and rectal cancer, but not colon cancer, is unclear. "It is possible that, with the progressive absorption of water from the stool during its passage through the colon, the ingested carcinogens from tobacco smoke become progressively more concentrated and deleterious to the colorectal epithelium," the researchers suggest.

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