The risk of bladder cancer for smokers has increased since the mid-1990s, with a risk progressively increasing to a level five times higher among current smokers in one state—New Hampshire—than that among nonsmokers in 2001–2004, according to a study in the Journal of the National Cancer Institute. The study also showed that among individuals who smoked the same total number of cigarettes over their lifetime, that smoking fewer cigarettes a day for more years may be more harmful than smoking more cigarettes a day for fewer years.
A news release notes that although it has been known for some time that cigarette smoking causes bladder cancer, the influence of various parameters of smoking history, including trends in risk over time, is unclear.
In the JNCI study, Dalsu Baris, MD, PhD, of the NCI's Division of Cancer Epidemiology and Genetics and colleagues from NCI, Dartmouth Medical School, and the departments of health for Maine, New Hampshire, and Vermont examined bladder cancer risk in relation to smoking practices based on data from a large, population-based case-control study conducted in those states from 2001 to 2004.
To examine changes in smoking-induced bladder cancer risk over time, the researchers compared odds ratios for New Hampshire residents in this study with those from two case-control studies conducted in New Hampshire by Margaret Karagas, PhD, of Dartmouth Medical School in 1994–1998 and 1998–2001.
Among New Hampshire residents, there was a statistically significant, progressive increase in bladder cancer risk among both former and current smokers compared with nonsmokers over each of the time periods.
The researchers said that this may be partly attributable to changes over time in the concentration of bladder carcinogens in cigarette smoke, as well as to 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,” Dr. Baris and her coauthors write.
“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, PhD, MPH, of Hollings Cancer Center and the Division of Biostatistics and Epidemiology of Medical University of South Carolina, and James R. Hebert, ScD, of the University's Cancer Prevention and Control Program and Department of Epidemiology and Biostatistics, note that given the substantial body of evidence linking bladder cancer and smoking, the most important aspect of the new finding is that the association has substantially increased from 1994 to 2004.
“The findings of Baris et al are provocative and…offer a testable hypothesis that warrants thorough investigation,” the editorial said. “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.”