Background Although cigarette smoking has consistently been shown to be positively related to the risk of adenomatous polyp development (benign neoplastic growth of epithelial tissue in the colon), most studies of cigarette smoking and the risk of colorectal cancer have been negative. However, in two large prospective studies in women and men, a statistically significant association between cigarette smoking and an increased risk of colorectal cancer was found, but only after more than 35 years of smoking.