Prostate cancer occurs when cells within the walnut-sized gland in the male reproductive system mutate and begin to multiply. This gland, called prostate, is located in front of the rectum and underneath the urinary bladder. It surrounds the tube, called urethra, which carries urine from the bladder and semen through the penis. The gland functions by helping in the production and storage of seminal fluid. The prostate gland has an average length of three centimeters and weighs about twenty grams.

Different types of cells can be found in the prostate, but cancer occurring in this part of the male reproductive system almost always starts with the grandular cells. Cancers that start in the grandular cells are called adenocarcinoma and 99 percent of prostate cancers are classified as adenocarcinoma.

The peripheral zone of the prostate is where cancer usually develops. Some studies have claimed that the development of cancer in the prostate starts with the occurrence of a condition called prostatic intraepithelial neoplasia (PIN). Although there are still no studies that can confirm that PIN is a cancer precursor, many doctors believe that this condition has a role in the development of cancer in the prostate.

PIN is a condition wherein changes in the microscopic appearance of prostate gland cells start to happen. These changes start to appear in men during their 20s and could continue to escalate as they grow older. In the initial stage of PIN, small clumps of cancer cells remain confined to normal prostate glands. Over time, though, they could multiply and spread to the surrounding prostate tissues and form a tumor. The tumor may grow and invade nearby organs and even metastasize to spread to other organs such as the bones and lymph nodes.

The specific cause of this condition has yet to be pinpointed by medical studies, but several factors have been associated with a man's risk of developing this condition such as age, genetics, race, lifestyle, diet and medications used. In terms of age, research figures have shown that the condition is not very common among men aged below 45. The chances of developing this condition, though, increase as a man ages. But since cancer in the prostate is slow to develop, some men who already have the condition might not show symptoms for years and might even die of other causes without the disease having affected them, particularly if this cancer is acquired during the latter stage of a man's life.

According to medical statistics, cancer of the prostate is the most common non-skin cancer in the United States. It has been projected that in 2006, 234,000 men will be diagnosed with cancer of the prostate in the United States alone and an estimated 27,000 men will die from the disease. Despite these seemingly scary figures, prostate cancer remains a much controllable condition compared with other types of cancer and the international medical community is continuing its efforts to improve methods of detecting the condition early to give men a better chance of managing it.