WASHINGTON Puffing on cigarettes increases the likelihood of bladder cancer for all smokers, but women who smoke face a much more acute risk than men, researchers said on Tuesday.

Researchers at the University of Southern California's Keck School of Medicine found that smokers overall run a risk 2 1/2 times higher of contracting bladder cancer than nonsmokers. But when comparable numbers of cigarettes are smoked, women experienced a much greater chance of developing bladder cancer than men, the researchers said.

Dr. Ronald Ross, chairman of Preventive Medicine at the Keck School's Norris Comprehensive Cancer Center, said the study provides the latest evidence of women's increased risk over men for some cancers caused by smoking. He pointed to the growing evidence that female smokers also incur a higher risk of lung cancer than male smokers.

"It does drive home the point that women are not escaping any of this smoking-related disease risk and, if anything, they're getting pounded by it even more perhaps than men. And I think that's an important point for women to take away from this," Ross said in an interview.

The findings also are surprising because doctors generally consider bladder cancer a man's disease. Bladder cancer accounts for 6 percent of all new cancer cases in men and 2 percent of new cancer cases in women.

Some 53,200 Americans were diagnosed with bladder cancer and the disease killed 12,200 last year, according to the American Cancer Society. about half of all cases are believed to be caused by smoking.

------------ Women's Risk Higher Across the Board ----------

The study, which appeared in the Journal of the National Cancer Institute, involved 1,514 patients with bladder cancer and 1,514 control subjects who live in the Los Angeles area.

The researchers questioned all the participants about general smoking habits, how many cigarettes they smoked and how often, as well as which types of cigarettes they smoked and whether they inhaled deeply, moderately or lightly.

For both men and women, the risk of bladder cancer increased both with the number of cigarettes smoked daily and with the number of years that the subjects smoked regularly, researchers said. In nearly every category of smoking, the risks to women were greater than those to men.

Looking at very heavy smokers, for example, the study found that women who smoked 40 or more cigarettes a day for 40 years or more faced more than twice the risk of contracting bladder cancer as men with the same smoking habits. These women incurred more than 11 times the risk of bladder cancer than a nonsmoker, while men ran approximately five times the risk of a nonsmoker.

Ross said doctors do not know exactly why smoking causes bladder cancer, but said it could be due to the presence in cigarette smoke of small amounts of a category of chemicals called arylamines.

The researchers analyzed blood samples from some of the study participants, looking for evidence of exposure to arylamines. They found that among men and women who smoked at the same level, concentrations of a certain indicator of exposure to arylamines were higher in women than in men.

Researchers found no difference in bladder cancer risk associated with filtered versus unfiltered cigarettes or low-tar versus high-tar cigarettes, nor any difference in risk tied to whether smokers reported deep or shallow inhalations.

The bladder is a hollow organ in the lower abdomen that stores urine after it passes from the two kidneys and before it is expelled from the body. About 90 percent of bladder cancers begin in the cells lining the bladder.

Heredity is not thought to be a factor in development of bladder cancer.

Researchers from the Massachusetts Institute of Technology also participated in the study.

(Reuter)