Smoking increased the risk for developing colon cancer, and female smokers may have a greater risk than male smokers, according to data published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.
"Globally, during the last 50 years, the number of new colon cancer cases per year has exploded for both men and women," said Inger Torhild Gram, M.D., Ph.D., professor in the Department of Community Medicine at the University of Tromsø in Norway. "Our study is the first that shows women who smoke less than men still get more colon cancer."
Gram and her colleagues examined the association between cigarette smoking and colon cancer, by tumor location, in a large Norwegian cohort of more than 600,000 men and women. The participants from four surveys initiated by the National Health Screening Service of the Norwegian Institute of Public Health had a short health exam and completed questionnaires about smoking habits, physical activity and other lifestyle factors. The participants were followed by linkage to the Cancer Registry of Norway and the Central Population Register. During an average 14 years of follow-up, close to 4,000 new colon cancer cases were diagnosed.
Gram and colleagues found that female smokers had a 19 percent increased risk compared with never-smokers, while male smokers had an 8 percent increased risk compared with never-smokers.
In addition, women who started smoking when they were 16 or younger and women who had smoked for 40 years or more had a substantially increased risk, by about 50 percent. Also, the dose-response association between the number of cigarettes smoked per day, number of years smoked and number of pack-years smoked and colon cancer risk was stronger for women than it was for men.
"The finding that women who smoke even a moderate number of cigarettes daily have an increased risk for colon cancer will account for a substantial number of new cases because colon cancer is such a common disease," said Gram. "A causal relationship between smoking and colorectal cancer has recently been established by the International Agency for Research on Cancer of the World Health Organization, but unfortunately, this is not yet common knowledge, neither among health personnel nor the public."
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