Prostate cancer is the most common cancer in men in the US, except for skin cancer. It mainly affects older men and is very common – about 13% of men will get it in their lifetime. The prostate is a walnut-sized gland in men by the base of the bladder that produces seminal fluid, which helps sustain and transport sperm. Prostate cancer occurs when cells in the gland change, causing abnormal growth and – like many cancers - it develops slowly over time and so may cause few, if any, symptoms initially. Prostate cancer is often confined within the prostate gland and causes little serious harm, although it may cause troublesome symptoms. However, it can spread to other organs and become life-threatening and so for this reason the sooner prostate cancer is found, the better the chances of treatment being effective.