Is smoking causing 15 to 25 percent of prostate cancer-specific deaths each year?

A new paper just published in European Urology offers further evidence from a meta-analysis of data from 51 different primary papers that smoking tobacco does increase a man’s risk of dying from prostate cancer — by about 24 percent compared to the risk for non-smokers.

This is not the first time that research has suggested an association between tobacco use and prostate cancer-specific mortality. However, it does appear to be somewhat more compelling than earlier studies.

The new paper by Islami et al. collates data from a carefully identified set of primary research articles that included a total of > 4 million cohort participants, 50,349 incident cases of prostate cancer, and 11,823 cases of prostate cancer-specific mortality.

They showed that, based on this meta-analysis:

  • Current cigarette smoking was associated with an increased risk of prostate cancer-specific mortality (relative risk [RR] = 1.24 compared to non-smokers).
  • The number of cigarettes smoked per day had a dose-response association with risk for prostate cancer-specific mortality (p = 0.02; RR for 20 cigarettes per day = 1.20).
  • The population attributable risk (PAR) for cigarette smoking and prostate cancer-specific mortality was
    • 6.7 percent in among men in the USA
    • 9.5 percent among European men
  • The PAR corresponds to > 10,000 deaths per annum in these two regions.

In addition, the authors showed that:

  • Current cigarette smoking was inversely associated with risk for a diagnosis of incident prostate cancer (RR = 0.90 compared to non-smokers), but there was high heterogeneity in the results for diagnosis from study to study.
  • In studies completed in 1995 or earlier (i.e., prior to the widespread PSA screening era), ever smoking showed a small positive association with risk for incident prostate cancer (RR = 1.06 compared to non-smoking), with little heterogeneity.

Islami et al. conclude that:

Combined evidence from observational studies shows a modest but statistically significant association between cigarette smoking and fatal [prostate cancer]. Smoking appears to be a modifiable risk factor for [prostate cancer] death.

They also conclude, from a patient perspective, that:

Smoking increases the chance of prostate cancer death. Not smoking prevents this harm and many other tobacco-related diseases.

In addition, according to a commentary on the study in Renal & Urology News, the authors write that:

Even if the association between smoking and [prostate cancer] death is established as causal, the magnitude of association is smaller versus those reported for other smoking-related cancers including cancers of the lung and upper aerodigestive tract. Therefore, the proportion of the [prostate cancer-specific] deaths attributed to smoking will be modest. However, because [prostate cancer] is a common cause of cancer death, this association may have a considerable impact on cancer mortality at the population level.

As noted above, the authors estimate that smoking may be associated with something north of 10,000 deaths per year in America and Europe. This would imply that smoking is the putative cause of something like 5,000 of the 28,000 prostate cancer-specific deaths each year or about 18 percent.

The one odd thing in this study is the finding that, while smoking was associated with a small increase in risk for a diagnosis of prostate cancer prior to the PSA era, there appears to be no such association since 1995 (and there may even have been a small decrease in risk). Of this finding, the authors write that the

reason for this pattern is unclear. One possible explanation is that smoking may reduce the risk of indolent, non-aggressive cancers that have predominated in more recent years while promoting more aggressive cancers.

However, any possible decrease in one’s risk for a diagnosis of prostate cancer associated with smoking as compared to not smoking is quite certainly outweighed by the increase in risk for prostate cancer-specific mortality — quite apart from the already well-known increases in risk for lung cancer, bladder cancer, and a host of other serious ailments.

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