What is prostate cancer?
To understand prostate cancer, it helps to know something about the prostate and nearby structures in the body.
About the prostate
The prostate is a gland found only in males. It is located in front of the rectum and below the urinary bladder. The size of the prostate varies with age. In younger men, it is about the size of a walnut, but it can be much larger in older men.
The prostate's job is to make some of the fluid that protects and nourishes sperm cells in semen, making the semen more liquid. 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.
The prostate starts to develop before birth. It grows rapidly during puberty, fueled by male hormones (called androgens) in the body. The main androgen, testosterone, is made in the testicles. The enzyme 5-alpha reductase converts testosterone into dihydrotestosterone (DHT). DHT is the main hormone that signals the prostate to grow.
The prostate usually stays at about the same size or grows slowly in adults, as long as male hormones are present.
Benign prostatic hyperplasia
The inner part of the prostate (around the urethra) often keeps growing as men get older, which can lead to a common condition called benign prostatic hyperplasia (BPH). In BPH, the prostate tissue can press on the urethra, leading to problems passing urine.
BPH is not cancer and does not develop into cancer. But it can be a serious medical problem for some men. If it requires treatment, medicines can often be used to shrink the size of the prostate or to relax the muscles in it, which usually helps with urine flow. If medicines aren't helpful, some type of surgery, such as a transurethral resection of the prostate (TURP) may be needed. (See the "Surgery for prostate cancer" section for a description of this procedure.)
Several types of cells are found in the prostate, but almost all prostate cancers develop from the gland cells. Gland cells make the prostate fluid that is added to the semen. The medical term for a cancer that starts in gland cells is adenocarcinoma.
Other types of cancer can also start in the prostate gland, including sarcomas, small cell carcinomas, and transitional cell carcinomas. But these types of prostate cancer are so rare that if you have prostate cancer it is almost certain to be an adenocarcinoma. The rest of this document refers only to prostate 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 diseases 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 doctors believe that prostate cancer starts out as a pre-cancerous condition, although this is not yet known for sure.
Prostatic intraepithelial neoplasia (PIN)
In this condition, there are changes in how the prostate gland cells look under the 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 their 20s. Almost half of all men have PIN by the time they reach 50. Many men begin to develop low-grade PIN at an early age but do not necessarily develop prostate cancer. The importance of low-grade PIN in relation to prostate cancer is still unclear. If a finding of low-grade PIN is reported on a prostate biopsy, the follow-up for patients is usually the same as if nothing abnormal was seen.
If high-grade PIN has been found on your prostate biopsy, there is about a 20% to 30% chance that you also have cancer in another area of your prostate. This is why doctors often watch men with high-grade PIN carefully and may advise them to have a repeat prostate biopsy, especially if the original biopsy did not take samples from all parts of the prostate.
Proliferative inflammatory atrophy (PIA)
This is another finding that may be noted on a prostate biopsy. 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: 08/26/2013
Last Revised: 02/24/2014