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Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer cells, and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?

Prostate cancer begins when cells in the prostate gland start to grow uncontrollably. The prostate is a gland found only in males. It makes some of the fluid that is part of semen.

The prostate is below the bladder and in front of the rectum. The size of the prostate changes with age. In younger men, it is about the size of a walnut, but it can be much larger in older men.

Just behind the prostate are glands called seminal vesicles that make most of the fluid for semen. The urethra, which is the tube that carries urine and semen out of the body through the penis, goes through the center of the prostate.

Types of prostate cancer

Almost all prostate cancers are adenocarcinomas. These cancers develop from the gland cells (the cells that make the prostate fluid that is added to the semen).

Other types of prostate cancer include:

  • Sarcomas
  • Small cell carcinomas
  • Neuroendocrine tumors (other than small cell carcinomas)
  • Transitional cell carcinomas

These other types of prostate cancer are rare. If you have prostate cancer it is almost certain to be an adenocarcinoma.

Some prostate cancers can grow and spread quickly, but most grow slowly. In fact, autopsy studies show that many older men (and even some younger men) who died of other causes also had prostate cancer that never affected them during their lives. In many cases neither they nor their doctors even knew they had it.

Possible pre-cancerous conditions of the prostate

Some research suggests that prostate cancer starts out as a pre-cancerous condition, although this is not yet known for sure. These conditions are sometimes found when a man has a prostate biopsy (removal of small pieces of the prostate to look for cancer).

Prostatic intraepithelial neoplasia (PIN)

In PIN, there are changes in how the prostate gland cells look under a microscope, but the abnormal cells don’t look like they are growing into other parts of the prostate (like cancer cells would). Based on how abnormal the patterns of cells look, they are classified as:

  • Low-grade PIN: the patterns of prostate cells appear almost normal
  • High-grade PIN: the patterns of cells look more abnormal

PIN begins to appear in the prostates of some men as early as in their 20s.

Many men begin to develop low-grade PIN when they are younger but don’t necessarily develop prostate cancer. The possible link between low-grade PIN and prostate cancer is still unclear.

If high-grade PIN is found in your prostate biopsy sample, there is about a 20% chance that you also have cancer in another area of your prostate.

Proliferative inflammatory atrophy (PIA)

In PIA, the prostate cells look smaller than normal, and there are signs of inflammation in the area. PIA is not cancer, but researchers believe that PIA may sometimes lead to high-grade PIN, or perhaps to prostate cancer directly.


Last Medical Review: 02/16/2016
Last Revised: 03/11/2016