An updated review of the epidemiological evidence that cigarette smoking increases risk of colorectal cancer

Carcinogens from tobacco reach the colorectal mucosa through either the ali mentary tract or the circulatory system and could possibly damage or alter expression of important cancer-related genes. Twenty-one of 22 studies foun d that long-term, heavy cigarette smokers have a 2-3-fold elevated risk of colorectal adenoma, Risk of large adenomas, immediate cancer precursors, wa s elevated in smokers in 12 of 12 studies. The studies of smoking and color ectal cancer risk conducted earlier in the twentieth century consistently d id not show any association. However, 27 studies in various countries, incl uding the vast majority of those that have been analyzed in the past severa l years, now show an association between tobacco use and colorectal cancer. In the United States, 15 of 16 studies conducted after 1970 in middle-age men and elderly men and, in the 1990s, in women demonstrate an association. This temporal pattern is consistent with an induction period of three to f our decades between genotoxic exposure and the diagnosis of colorectal canc er and with men as a group having begun smoking several decades earlier tha n women. Overall, accumulating evidence, much within the past decade, stron gly supports the addition of colorectal cancer to the list of tobacco-assoc iated malignancies and the possibility that up to one in five colorectal ca ncers in the United States may be potentially attributable to tobacco use.