Aug. 16, 2011 -- Smoking may increase risk for bladder cancer even more than previously believed, and this risk is comparable among male and female smokers. The new study appears in the Aug. 17 issue of the Journal of the American Medical Association.
“Changing the composition of cigarettes may be associated with the strengthening of the association between smoking and bladder cancer risk,” says study author Neal D. Freedman, PhD, MPH, an investigator at the National Cancer Institute in Rockville, Md.
Tobacco, Cigarettes Changed Over Time
Exactly which additions or subtractions may have increased the already heightened risk is not known because in the past 50 years there have been a number of changes in the type of tobacco, the way it is prepared, and how cigarettes are constructed. Many manufacturers have cut back on tar and nicotine but replaced these with other potential carcinogens such as beta-naphthylamine, which is a known to increase bladder cancer risk.
“Future studies should try to replicate these findings and analyze the constituents of tobacco smoke and identify the components that may have led to this increase,” he says.
The new study looked at close to 500,000 people who answered questions regarding their lifestyle including smoking status between Oct. 25, 1995, and Dec. 31, 2006. Of these, 3,896 men and 627 women developed bladder cancer during follow-up.
Former smokers were 2.2 times more likely to develop bladder cancer than people who never smoked.
Current smokers were four times more likely to develop bladder cancer than people who never smoked, the study showed.
The risks seen in the new study superseded those seen in an accompanying literature review of seven studies that looked at the same association among current smokers.
According to the new estimates, history of current or past smoking comprises 50% of bladder cancer risk among men and 53% of risk seen among women. By contrast, smoking explains 90% of lung cancer, Freedman says.
“There is a genetic component to bladder cancer risk, and there is also an important occupational component,” he says. Certain occupations such as painters, truck drivers, and machinists may increase risk of bladder cancer because of on-the-job exposures.
Men are also are greater risk for bladder cancer than women. “Even among never smokers, men are four times more likely to develop bladder cancer than women,” he says.
Quit Smoking, Lower Bladder Cancer Risk
The findings should “emphasize the importance of preventing people from smoking at all or if they do smoke, emphasize the importance of quitting,” he says.
Quitting smoking can make a difference in bladder cancer risk, he says.
“The shorter amount of years you smoke, and the earlier you quit, the better in terms of reducing your bladder cancer risk,” he says.
“Patients are always surprised about the link between smoking and bladder cancer,” says Elizabeth Kavaler, MD, a urologist at Lenox Hill Hospital in New York City.
Environmental toxins including some found in cigarettes may alter the genetic material in the bladder wall, increasing cancer risk, she says.
“It is a two-hit theory,” she says. “Patients would have a genetic predisposition to bladder cancer and then smoking on top of this creates the second hit,” she says.