Detection is tricky because of where the prostate is located. It is a bulb-shaped gland that goes round the urethra just where it leaves the bladder, so when it swells up urination becomes a problem.
In fact, the first symptoms include finding it hard to urinate, wanting to urinate often, a burning sensation when you do, or blood in the urine. But cases often aren't spotted until quite late because the basic method of diagnosing an enlarged prostate is my rectal examination and many men prefer to avoid that. For cancers there is now a prostate-specific antigen test.
The prostate's job is to add acids, trace elements, and enzymes to seminal fluid at the moment of ejaculation; these activate the sperm and give semen its distinctive smell. For reasons we don't understand the prostate tends to enlarge and stiffen with age, but is probably connected with changing levels of various hormone. About a third of cases clear up of their own accord, but an enlarged prostate can cause related infection in the bladder and the kidneys.
In cancer cases doctors are increasingly recognizing a connection with high-fat diets. Cancer of the prostate is rare in Japan and China, for instance, where low-fat diets containing lots of vegetables and fish are the norm.