Bladder cancer risks increase over time for smokers

(Ivanhoe Newswire) -- It's well established that cigarette smoking causes bladder cancer, but the influence of smoking history over time has been unclear.

Dalsu Baris, M.D., Ph.D., of the Division of Cancer Epidemiology and Genetics, National Cancer Institute, in Bethesda, Md., and colleagues examined bladder cancer risk in relation to smoking practices based on data from a population-based case--control study conducted in Maine, New Hampshire, and Vermont from 2001 to 2004.

The researchers found that since the mid-1990s, risk of bladder cancer for smokers in New Hampshire has increased to a level five times higher among current smokers than that among nonsmokers in 2001-2004. They also found that smoking fewer cigarettes per day for more years may be more harmful than smoking more cigarettes per day for fewer years.

Among New Hampshire residents, there was a statistically significant increase in bladder cancer risk among both former and current smokers compared with nonsmokers over each time period. According to the authors, this may be partly attributable to changes over time in the concentration of bladder carcinogens in cigarette smoke, as well as the introduction and increased popularity of low-tar/low-nicotine cigarettes. Smokers who switch to low-tar/low-nicotine cigarettes are thought to increase the depth and frequency of inhalation to satisfy the need for nicotine.

"The observed relationship between smoking and bladder cancer risk was stronger than reported in earlier studies, with statistically significant trends in risk with increasing duration, intensity, and pack-years for both men and women," the authors wrote. "Additional modeling of the rate of delivery of cigarette smoke supports previous observations, suggesting a greater risk of bladder cancer for total exposure delivered at a lower intensity for longer duration than for an equivalent exposure delivered at a higher intensity for shorter duration."

In an accompanying editorial, Anthony J. Alberg, Ph.D., MPH, of the Hollings Cancer Center and Division of Biostatistics and Epidemiology, Medical University of South Carolina in Charleston, and James R. Hebert, ScD, of the Department of Epidemiology and Biostatistics at the University of South Carolina in Columbia, note that the most important aspect of this finding was that the association between smoking and bladder cancer increased substantially from 1994 to 2004. Alberg and Hebert agree that the data suggest that an increase in the carcinogenic content of cigarettes over time may be partly responsible.

"The findings of Baris et al. are provocative and-- offer a testable hypothesis that warrants thorough investigation," the editorialists wrote. "More precisely, pinpointing the specific role of cigarette additives will be an important element of this research. This study highlights the need for continued vigilance in monitoring the impact of the changing cigarette on disease risk."

SOURCE:Journal of the National Cancer Institute, November 16, 2009

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