Bladder Cancer Risk From Smoking Higher Than Expected

Roxanne Nelson

August 16, 2011

August 16, 2011 — The risk for bladder cancer among smokers appears to be higher than previously reported, according to new data from a large prospective trial. In addition, the risk was found to be similar for both male and female smokers.

The new finding is reported in the August 17 issue of the Journal of the American Medical Association.

As compared with never-smokers, both former and current smokers had an increased risk for bladder cancer. Former smokers had a 2.2 times increased risk for bladder cancer, and current smokers had a risk that was approximately 4 times higher relative to never-smokers.

The authors point out that their data differ from the summary risk estimate of 2.94 for current smokers, which was observed in 7 previous studies.

"The take-home message of our study should be that smoking is strongly associated with bladder cancer risk," lead author Neal D. Freedman, PhD, MPH, an investigator at the National Cancer Institute, told Medscape Medical News. "Our results emphasize the importance of preventing smoking initiation, and among current smokers, smoking cessation."

"There are many different carcinogens in cigarette smoke," he added. "Thus, the best public health approach is for people to never smoke, and if they smoke, to quit."

Established Risk Factor

Smoking is the "best established" risk factor for bladder cancer for both men and women, say the authors. Past research has shown that the population attributable risk for bladder cancer for smoking is 50% to 65% in men and 20% to 30% in women, and individuals who are current smokers face triple the risk as compared with those who never smoked.

But although the rate of bladder cancer has remained relatively stable in the United States for the past 3 decades, the prevalence of smoking has substantially declined. However, the authors point out that the composition of cigarettes has changed during the past half-century. While the concentration of tar and nicotine has decreased in cigarette smoke, there has also been an apparent increase in the concentration of a number of carcinogens, including beta-naphthylamine, which is a known bladder carcinogen. Epidemiologic studies have also observed higher relative risks associated with cigarette smoking for lung cancer, concurrent with these changes in the make-up of cigarette smoke.

Thus, changes in the composition of cigarette smoke may be associated with a rising risk for bladder cancer, similar to what has been documented for lung cancer.

Study Details

The study analyzed data from men (n = 281,394) and women (n = 186,134) enrolled in the National Institutes of Health-AARP (NIH-AARP) Diet and Health Study. All participants completed a lifestyle questionnaire and were followed between October 1995 and December 2006.

Over 4,518,941 person-years of follow-up, bladder cancer was newly diagnosed in a total of 3896 men and 627 women. This extrapolated to incidence rates of 144.0 per 100,000 person-years in men and 34.5 per 100,000 person-years in women.

The authors found that cigarette smoking was a strong risk factor for bladder cancer in both sexes.

Both former smokers (119.8 per 100,000 person-years; hazard ratio, 2.22) and current smokers (177.3 per 100,000 person-years; hazard ratio, 4.06) had higher risks for bladder cancer as compared with never-smokers (39.8 per 100,000 person-years).

As seen in previous studies, smoking cessation was associated with lower rates of bladder cancer risk in both sexes. More specifically, individuals who had quit for 10 years or longer before baseline had lower incidence rates of bladder cancer than those who quit 1 to 4 years or 5 to 9 years before baseline. However, as compared with never-smokers, the relative risks remained even for those who had quit smoking 10 years or more before baseline.

The authors also performed a systematic review and meta-analysis of 7 previously published prospective cohort studies that evaluated the association between current cigarette smoking and incident bladder cancer. The studies were begun between 1963 and 1987, and the summary risk estimate of 2.94 was lower than observed in the current paper. They note that no evidence of publication bias was observed.

The study was supported by the National Institutes of Health. The authors have disclosed no relevant financial relationships.

JAMA. 2011;306:737-745.

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