By
The Associated Press
WASHINGTON - Women smokers may face a higher risk of bladder cancer than men who smoke the same amount, a new study suggests. Some cancer experts, however, are skeptical about the findings.
Scientists have long warned that American smokers are two to three times more likely to get bladder cancer than nonsmokers are.
University of Southern California researchers began comparing bladder cancer rates between smokers in different parts of the world when they spotted something unusual. In their study, the American women who smoked seemed at higher risk than men.
"I'll be the first to admit it is counterintuitive," said study co-author Ronald Ross, chairman of preventive medicine at the USC/Norris Comprehensive Cancer Center. Overall, bladder cancer strikes far more men than women.
Ross' research team then compared the smoking habits of 1,514 Los Angeles-area bladder cancer patients with 1,514 similar but cancer-free people.
Cigarette smokers were 2.5 times more likely than nonsmokers to get bladder cancer, the team reported yesterday in the Journal of the National Cancer Institute. Risk increased with length of time smoking and number of daily cigarettes - filtered or low-tar cigarettes weren't safer.
For almost every amount of cigarettes smoked, women's risk was a little higher than men's - a statistically significant increase, Ross said. For the heaviest smokers - 40 cigarettes a day for 40 years - women's risk was twice that of men's.
But Ross wasn't convinced until he analyzed blood tests performed on 1,300 study participants. The bodies of women smokers harbored more metabolites of tobacco-carried chemicals called arylamines, believed to spur smoking-caused bladder cancer, the study found.
"It suggests that women somehow either activate or detoxify these (chemicals) differently than men do," Ross said. "The question for us now is: Why does that occur?"
American Cancer Society epidemiologist Michael Thun urged caution, because in general bladder cancer occurs four times more frequently in men than women.
While smoking isn't bladder cancer's only cause, men's higher disease rate "makes it implausible that smoking poses a greater risk in women," Thun said.
Also, this type of study, known scientifically as a "case-control," can overestimate women's risk, Thun said.
"The main point is how high the risk is for long-term smokers" regardless of gender, he stressed.
But Ross said other studies suggest women smokers may face a higher risk of lung cancer than male smokers, so gender differences in bladder cancer, too, make sense.
The USC researchers also are investigating smokers in China, who get lung cancer just as readily as American smokers but seem to have a lower bladder cancer risk. Add that quandary to the U.S. gender finding and "there's really something fundamental about the smoking-bladder cancer relationship that we really don't understand," Ross contended.
About 54,300 Americans will be diagnosed with bladder cancer this year, and 12,400 will die, the cancer society estimates. Government statistics show smoking kills over 400,000 Americans a year, from numerous cancers, heart diseases and lung diseases.
