Smoking implicated in half of female bladder cancers

Current cigarette smokers have a higher risk of bladder cancer than previously reported, and the risk in women is comparable to that in men, say the authors of a study from the National Cancer Institute, Bethesda, MD.

The study, which was published in JAMA (2011; 306:737-45), includes data from more than 450,000 participants in the National Institutes of Health-AARP Diet and Health Study, a questionnaire-based study initiated in 1995 with follow-up through the end of 2006.

The authors say the data indicate that smoking is responsible for about half of female bladder cancer cases, similar to the proportion found in men in current and previous studies. The increase in the proportion of smoking-attributable bladder cancer cases among women may be a result of the increased prevalence of smoking by women, so that men and women are about equally likely to smoke, as observed in the current study and in the U.S. population overall, according to surveillance by the Centers for Disease Control and Prevention.

"Current smokers in our study had a fourfold excess risk of developing bladder cancer, compared to a threefold excess risk in previous studies. The stronger association between smoking and bladder cancer is possibly due to changes in cigarette composition or smoking habits over the years," said first author Neal Freedman, PhD. "Incidence rates of bladder cancer in the United States have been relatively stable over the past 30 years, despite the fact that smoking rates have decreased overall. The higher risk, as compared to studies reported in the mid- to late-1990s, may explain why bladder cancer rates haven’t declined."

In the current study, former smokers were twice as likely to develop bladder cancer as never smokers, and current smokers were four times more likely than those who never smoked. As with many other smoking-related cancers, smoking cessation was associated with reduced bladder cancer risk. Participants who had been smoke-free for at least 10 years had a lower incidence of bladder cancer compared with those who quit for shorter periods of time or who still smoked.