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Secondhand Smoke and Bladder Cancer: What’s the Connection?

The relationship between bladder cancer and smoking has typically been investigated and tied to the smoking history of the patient. But there is now research that suggests that secondhand smoke also plays a role in increasing the likelihood of developing bladder cancer in non-smokers.

"What if I don’t smoke?"

The questions investigators have been asking are:

  1. Is exposure to secondhand smoke a confirmed risk factor increasing the rate of developing bladder cancer?
  2. Does exposure to secondhand smoke in childhood contribute to lifetime exposure, resulting in a higher rate of bladder cancer?

The investigators’ approach to answer these questions was to conduct a meta-analysis, an examination of data from previous independent studies on the same subject, designed to determine overall trends in the literature available.

Researching secondhand smoke and bladder cancer

There have been clinical studies that looked to identify the relationship between secondhand smoke and bladder cancer. In earlier reviews, only one report found “a significantly increased risk of secondhand smoke and bladder cancer in nonsmoking population.”1 A new meta-analysis out of China was conducted evaluating 14 other studies that went through a rigorous review for terms of inclusion in the study. The literature review from which the reports were gleaned included studies published between 1986-2012 addressing a population of over 325,000 people, including over 4,000 cases and over 320,000 controls.

An increased risk of bladder cancer

The findings concluded that there was a 22% increased risk of bladder cancer for lifetime secondhand smoke exposure in nonsmoking patients compared with a nonsmoking population who was not subject to secondhand smoke exposure.1 A second meta-analysis was carried out to evaluate childhood exposure to secondhand smoke and the risk of bladder cancer. An even higher rate of increased risk of 43% was identified, but there were some potential bias issues in some of the prior evaluations.1 So, although it appears that exposure to secondhand smoke during childhood creates a statistically significant higher risk for bladder cancer, the statistical results may not reliable and require further evaluation.1

Carcinogens in secondhand smoke

The smoking population has a four-fold risk of bladder cancer compared with nonsmokers. We know that tobacco contains over 60 kinds of carcinogens that are typically cleaned from the body through the blood and urinary tract. The study findings suggest that secondhand smoke may also contain the same carcinogens, and which activate the disease development pathways. Additional basic experiments should be carried out in order to confirm the role of secondhand smoke in the formation of bladder cancer.

More research is needed

This comprehensive meta-analysis indicated a statistically significant increased risk of bladder cancer for lifetime secondhand smoke exposure. Further research should be conducted to confirm the association and to identify and clarify the biological mechanisms that may be responsible.1

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