Causes: in many cases there is no obvious cause. 
Genetics: A family history of prostate cancer increases your risk. A strong family history of breast cancer predisposes a man to prostate cancer. Presumably the same faulty gene is involved.
Age: The risk rises with age. It is rare under age 50 but increases with each decade. Some researchers believe that if a man lives long enough he will develop prostate cancer - but he might have to live to 120 years old!
Race: African-American or African-Caribbean raises the risk: Asian lowers the risk
Diet: High fat diet may increase risk. Increased dairy intake increases risk. Increased calcium increases risk. Licopene (tomatoes) decreases risk. Soy decreases risk. MORE ON DIET.
 

Symptoms.
There are no symptoms in the early stages. Some men never have symptoms. Often it is found on routine annual lab work (PSA test).
The symptoms are similar to BPH, Benign Prostatic Hypertrophy, enlargd prostate and are the result of the swollen prostate pressing on the outlet of the bladder (urethra). They include difficulty starting or stopping urination, dribbling, frequency of urination (because the bladder does not empty completely),  nocturia (having to get up at night more often). There may be pain on orgasm. Rarely there is blood in the urine. Unfortunately some men discover that they have cance when they have syptoms of spread (metastases) of the cancer locally in the lower abdomen, or distantly such as back pain from bone involvement.