Prevention is an important treatment strategy for diminishing prostate cancer 
morbidity and mortality and is applicable to both early- and late-stage disease. 
There are three basic classifications of cancer prevention: primary (prevention 
of incident disease), secondary (identification and treatment of preclinical 
disease), and tertiary (prevention of progression or recurrence). Based on level 
I evidence, 5-alpha reductase inhibitors (5-ARIs) should be considered in 
selected men to prevent incident prostate cancer. Level I evidence also supports 
the consideration of dutasteride, a 5-ARI, for tertiary prevention in active 
surveillance and biochemical recurrence patients. Vitamins and supplements, 
including selenium or vitamin E, have not been proven in clinical trials to 
prevent prostate cancer and in the case of Vitamin E has been found to increase 
the risk of incident prostate cancer. Ongoing and future trials may further 
elucidate the role of diet and immunotherapy for prevention of prostate cancer.