Prostate cancer occurs when a malignant tumor forms in the tissue of the prostate, According to the National Cancer Institute  more than 186,000 American men are diagnosed with the disease each year. Prostate cancer is the second most common type of cancer among men in this country. The majority of the men diagnosed with prostrate cancer are over 65 years of age.
The prostrate is a gland about the size of a walnut in the male reproductive system that makes the fluid for semen.    One way doctors discover prostrate cancer is by looking at the level of a substance called prostate specific antigen (PSA).  PSA is often high in men with prostate cancer, but there are other reasons for this. Older males should are recommended to have PSA tests during check ups.
There are several signs of prostrate cancer, which include:
- Problems passing urine including pain and dribbling.
- Problems starting or stopping the stream, or dribbling 
- Low back pain 
- Pain with ejaculation
For more information:
Cancer 
http://www.nlm.nih.gov/medlineplus/prostatecancer.html