While it has never been directly shown that smoking causes prostate cancer, studies have shown that smoking is associated with higher rates of prostate cancer. In addition, studies have shown that men who smoke have a greater risk of dying of their prostate cancer.
Not only that, but it has also been shown that men who were formerly smokers also have an increased risk of developing prostate cancer, and those men who are the heaviest smokers have an almost 30% increased risk of dying of their prostate cancer than nonsmokers.
So, overall, there is plenty of evidence linking an increased risk of developing prostate cancer to smoking, and there is plenty of evidence linking poor outcomes after being diagnosed with prostate cancer to smoking.
Huncharek M, Haddock KS, Reid R, et al. Smoking as a Risk Factor for Prostate Cancer: A Meta-Analysis of 24 Prospective Cohort Studies. American Journal of Public Health, April 2010, Vol 100, No. 4