An analysis of data that includes nearly 500,000 individuals indicates that the risk of bladder（膀胱） cancer among smokers is higher than reported from previous population data, and that the risk for women smokers is comparable with that of men, according to a study in the August 17 issue of JAMA. More than 350,000 individuals are diagnosed with bladder cancer per year worldwide, including more than 70,000 per year in the United States. Tobacco smoking is the best established risk factor for bladder cancer in both men and women, with previous studies indicating that current cigarette smoking triples bladder cancer risk relative to never smoking, according to background information in the article. "However, the composition of cigarettes has changed during the past 50 years, leading to a reduction in tar（焦油） and nicotine concentrations in cigarette smoke, but also to an apparent increase in the concentration of specific carcinogens, including beta-napthylamine, a known bladder carcinogen …," the authors write. They add that changing smoking prevalence and cigarette composition warrant revisiting risk estimates for smoking and bladder cancer.

Neal D. Freedman, Ph.D., M.P.H., of the National Cancer Institute, Department of Health and Human Services, Rockville, Md., and colleagues conducted a study to examine the association between tobacco smoking and bladder cancer using data from men (n = 281,394) and women (n = 186,134) in the National Institutes of Health-AARP (NIH-AARP) Diet and Health Study, who completed a lifestyle questionnaire and were followed up between October 1995 and December 2006. Previous studies of smoking and incident bladder cancer were identified by systematic review of the available literature.

During the course of follow-up, 3,896 men and 627 women were newly diagnosed with bladder cancer. Cigarette smoking was a significant risk factor for bladder cancer in both sexes. Relative to never smokers, former and current smokers had increased risk of bladder cancer in both men and women. Analysis of the data indicated that former smokers had a 2.2 times increased risk of bladder cancer and that for current smokers, the risk was about 4 times higher, relative to never smokers. "In contrast, the summary risk estimate for current smoking in 7 previous studies (initiated between 1963 and 1987) was 2.94," the authors write.

Ever smoking explained a similar proportion of bladder cancer in both sexes, with population attributable risks of 50 percent in men and 52 percent in women.

The researchers write that factors that may have strengthened the cigarette smoking-bladder cancer association include changes in the constituents of cigarette smoke (such as increased concentrations of beta-napthylamine), and increased awareness of bladder cancer risk in smokers, which may prompt earlier diagnostic workup.

"These results support the hypothesis that the risk of bladder cancer associated with cigarette smoking has increased with time in the United States, perhaps a reflection of changing cigarette composition. Prevention efforts should continue to focus on reducing the prevalence（流行，普遍） of cigarette smoking."