Smoking and bladder cancer. The modifying effect of cigarettes on other factors.

A population-based, incidence case-control study was used to assess the effect of cigarette smoking on other risk factors for the development of bladder cancer. White men (n = 332) between the ages of 21 and 84 with bladder cancer were compared with 686 population-based controls. Cigarette smokers were classified by current smoking status as well as by amount, duration, inhalation patterns, age at first having smoked, and years since having stopped smoking. These variables were associated with a change in the risk for bladder cancer. The population-attributable risk associated with cigarette smoking was 48.5%. Risks from the use of other tobacco products such as cigars, pipes, snuff, and chewing tobacco, and from caffeinated coffee, tea, and alcoholic beverages were evaluated in light of cigarette smoking status. Cigarette smoking was shown to be both a confounder and an effect modifier. Risk estimates for bladder cancer associated with caffeinated coffee and alcoholic beverages were decreased after controlling for the effects of cigarette smoking. However, an increased risk of developing bladder cancer from cigar smoking (Odds ratio [OR] = 2.46) and tea drinking (OR = 3.14) was only seen in men who never smoked cigarettes. An increased but not significant risk was also seen for pipe, snuff, and chewing tobacco use in noncigarette smokers. The population-attributable risk from cigars and tea in the population of white men who had never smoked was 6.3% and 18.9%, respectively. Our results suggest that cigarette smoking may obscure other risk factors unless those who never smoked are separately studied.