Smoking and colorectal cancer: different effects by type of cigarettes?
Although smoking is suggested to be a risk factor for colorectal cancer, the evidence to date is conflicting and may be confounded. Moreover, the effect of tobacco smoke may vary by time since initiation, type of tobacco product, anatomic subsites, and among ethnic groups. Data were derived from two consecutive population-based case-control studies conducted among Caucasians, Japanese, Native Hawaiians, Filipinos, and Chinese in Hawaii, including 1,959 ethnicity-, sex-, and age-matched case-control pairs. A lifetime history of smoking for different tobacco products and information on other risk factors were obtained by in-person interviews. Odds ratios (OR) and corresponding 95% confidence intervals (95% CI) were estimated using conditional logistic regression models with adjustment for potential confounders. Subjects who ever smoked were at an increased risk of colorectal cancer compared with never smokers (OR, 1.23; 95% CI, 0.99-1.52 for men and OR, 1.27; 95% CI, 1.01-1.59 for women). Increasing quartiles of pack-years over all tobacco products showed a clear dose-dependent association in men [for the highest quartile, Q4 (>40 pack-years) versus never smokers: OR, 1.48; 95% CI, 1.12-1.96; P(trend) = 0.002]. The dose-response trend was also present in women [for the highest quartile, Q4 (>30 pack-years) versus never smokers: OR, 1.38; 95% CI, 0.91-1.95; P(trend) = 0.04] and each ethnic group. There was a suggestion of a difference in risk with type of tobacco product. Non-filtered cigarettes increased risk of both colon and rectal cancer [for Q4 versus never smokers: OR, 1.59; 95% CI, 1.15-2.21; P(trend) = 0.001 and OR, 1.84; 95% CI, 1.18-2.86; P(trend) = 0.02, respectively], whereas filtered cigarettes seemed to increase risk of rectal but not colon cancer (OR, 1.37; 95% CI, 0.88-2.13; P(trend) = 0.06 and OR, 1.05; 95% CI, 0.79-1.39; P(trend) = 0.98, respectively). The effect of smoking was not limited to the distant past, and accumulated pack-years of smoking seemed to be more important than the time in which smoking occurred. The data from this large study corroborate previous reports of a positive association between smoking and colorectal cancer and suggest that the association may vary by type of cigarette.