​Reducing Bladder Cancer Risk

A large study of postmenopausal women showed strong benefit from smoking cessation in lowering the risk of bladder cancer.

Bladder cancer is the most common malignancy of the urinary system. Some 80,470 new diagnoses and 17,500 deaths from the disease are expected in the United States in 2019, according to National Cancer Institute estimates.

Bladder cancer is also a type of cancer with a well-established risk factor: smoking.

A study recently published in Cancer Prevention Research, a journal of the American Association for Cancer Research, indicated that quitting cigarette smoking was associated with significantly reduced risk of bladder cancer in postmenopausal women. The most significant reduction in risk occurred in the first 10 years after quitting, with a modest but continued decline in risk in later years.

The study’s lead author, Yueyao Li, MSPH, MD, a PhD candidate in the Department of Epidemiology and Biostatistics, School of Public Health, Indiana University in Bloomington, said that while bladder cancer is more common in men, women often have worse outcomes, even when diagnosed at similar stages.

In order to examine the relationship between smoking and bladder cancer risk in women, Li and colleagues examined data from the Women’s Health Initiative, a long-term national health study of postmenopausal women. They included data from 143,279 women, all of whom had supplied information on whether they had ever smoked cigarettes, how much they had smoked, and whether they were current smokers. In all, 52.7 percent of the women were categorized as "never smokers," 40.2 percent as former smokers, and 7.1 percent as current smokers.

As of Feb. 28, 2017, the researchers had identified 870 cases of bladder cancer. The study showed that, in comparison to never smokers, former smokers had twice the risk of bladder cancer, and current smokers had more than three times the risk.

The researchers performed analysis using various statistical models to analyze the association between years since quitting smoking and the risk of bladder cancer, and to account for variables such as education, race/ethnicity, BMI, and dietary factors. They found that the steepest reduction in risk occurred in the first 10 years after quitting smoking, with a 25 percent drop. The risk continued to decrease after 10 years of quitting, but even after 30 or more years since quitting smoking, risk remained higher for women who had smoked than those who never did.

However, in time-updated models that reflected those who stopped smoking during the study period, the researchers found that compared with women who continued to smoke, those who quit smoking during the follow-up years had a 39 percent decrease in bladder cancer risk, and the risk continued to decline over time.

Li said that while the biological mechanisms of the association between bladder cancer and smoking are not fully known, the study results indicate that women of any age should be discouraged from smoking, and even those who have smoked for many years stand to benefit from quitting. 

"Our study emphasizes the importance of primary prevention (by not beginning to smoke) and secondary prevention (through smoking cessation) in the prevention of bladder cancer among postmenopausal women," Li said. "Current smokers should be advised to quit smoking in order to reduce the risk of bladder cancer."

Li cautioned that the study was based on postmenopausal women, so results may not be fully generalizable. Also, exposure to smoking was self-reported.

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