Cigarette smoking and risk of cancers of the colon and rectum: A case-control study from Italy

The relationship between smoking habit and risk of colon and rectal cancers was considered in a case-control study conducted between 1991 and 1996 in six Italian centers. Cases were 1225 patients below age 75 with histologica lly confirmed cancer of the colon and 728 with cancer of the rectum. Contro ls were 4154 patients admitted to hospital far a wide spectrum of acute, no n-neoplastic diseases. Compared to neversmokers, the odds ratios (OR) for c urrent smokers of 25 or more cigarettes/day was 0.90 for patients with colo n and 0.86 for those with rectal cancer and those for ex-smokers were 1.02 and 1.09 for colon and rectal cancer, respectively. No increase in risk was found with duration of the habit, the OR for 40 or more years being 0.79 f or colon and 0.87 for rectal cancer. Furthermore, no relationship was appar ent with time since starting (the OR for 40 or more years were 0.94 for col on and 1.05 for rectal cancer), or age at starting (the OR for < 18 years w ere 1.02 for colon and 1.01 for rectal cancer), or for pack-years smoked (t he OR for 40 or more pack-years were 0.93 for colon and 0.91 for rectal can cer) or time since stopping among ex-smokers. No increase in risk was found in smokers of greater than or equal to 15 cigarettes/day for 40 years or l onger (OR: 0.93). No significant heterogeneity was found across strata of a ge at diagnosis, sex, education, physical activity at work, intake of alcoh ol, coffee, vegetables, total energy, and number of meals/day. Likewise, no significant association was apparent for various intestinal subsites. Thus , this study did not find cigarette smokers at higher risk for cancer of th e bowel even after a long duration and a long period since starting.