Female Smokers' Bladder Cancer Risk Now Equals That of Males
Cigarette smoking has long been linked to bladder cancer, but the risk of the disease developing appears to have climbed higher over the last several decades, especially among women who regularly light up, a large U.S. study has determined.
The study by the U.S. National Cancer Institute, which tracked almost 500,000 people over 11 years, found the likelihood of a smoker getting bladder cancer is about four times higher than someone who has never smoked.
Furthermore, the risk for female smokers now equals that for male tobacco users, according to the study published in this week's edition of the Journal of the American Medical Association.
"So in our study, 50 per cent of bladder cancer in men and 50 per cent of bladder cancer in women was explained by smoking," said Neal Freedman, an NIH investigator who led the research.
Earlier epidemiological research, some of it going back to the 1960s and '70s, had estimated the "population attributable risk" at 50 to 60 per cent for male smokers and 20 to 30 per cent for their female counterparts, Freedman said Tuesday from Rockville, Md.
"But previous studies generally occurred in populations where women smoked less than men," he said. "And so (now) in the U.S. population and most of the western world -- I'm not certain about Canada, but I believe also -- men and women smoke relatively similar amounts."
Interestingly, the incidence of bladder cancer has remained relatively stable over the last 30 years, at the same time that overall smoking rates in Canada and the U.S. have declined.
In Canada, 7,200 cases of bladder cancer are expected to be diagnosed this year -- 5,400 men and 1,800 women. About 1,850 people will die from the disease, Canadian Cancer Society estimates predict.
"The higher risk, as compared to studies reported in the mid- to late-1990s, may explain why bladder cancer rates haven't declined," said Freedman, noting that there may be other factors at work that complicate the picture.
Cigarettes and the smoke they produce have changed over the last 50 years, both in content and preparation, he pointed out. While amounts of tar and nicotine have been reduced, there have been apparent increases in concentrations of certain carcinogens, including beta-napthylamine, a known bladder cancer-causing agent.
"In addition to that carcinogen there are many more, and all or some may play a role in bladder cancer."
To conduct the research, Freedman and colleagues used data from the National Institutes of Health-AARP Diet and Health Study, in which almost 500,000 men and women completed a lifestyle questionnaire and were followed up between October 1995 and December 2006.
During that period, 3,896 men and 627 women were newly diagnosed with bladder cancer. The researchers found that former smokers were twice as likely as people who never used tobacco to develop bladder cancer. Those who had been smoke-free for at least 10 years had a lower incidence than those who quit for shorter periods or who still smoked.
"This emphasizes the importance of cigarette smoking in bladder cancer," said Freedman. "And I think our work emphasizes the importance of preventing smoking initiation, and among people that smoke, quitting smoking.
"And that will have a really important effect on preventing bladder cancer."
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