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About the prostate
The prostate is a walnut-sized gland located in front of the
rectum and underneath the urinary bladder. It is found only in men. The
prostate's job is to make some of the fluid that protects and nourishes
sperm cells in semen. Just behind the prostate gland are the 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, runs through the prostate.
The prostate starts to develop before birth and continues to
grow until a man reaches adulthood. This growth is 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 signals the prostate to grow. The prostate stays at adult
size in adults as long as male hormones are present. In older men, the
inner part of the prostate (around the urethra) often keeps growing,
leading to a common condition called benign prostatic hyperplasia
(BPH). In BPH, the prostate tissue can press on the
urethra, leading to problems passing urine. Although BPH can be a
serious medical problem, it is not cancer.
Prostate cancer
Several types of cells are found in the prostate, but over 99%
of 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 because these other types of prostate cancer are so
rare, 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 of
them 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 these
studies, 70% to 90% of the men had cancer in their prostate by age 80,
but in many cases neither they nor their doctors even knew they had it.
Pre-cancerous conditions of the prostate
Many doctors believe that prostate cancer begins with a
pre-cancerous condition called prostatic
intraepithelial neoplasia (PIN). 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. 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). The cell changes are classified
as either low-grade, meaning the patterns of prostate cells appear
almost normal, or high-grade, meaning they look more abnormal.
If you have had high-grade PIN found on a prostate biopsy,
there is about a 20% chance that you also have cancer in your prostate.
For this reason, doctors often watch men with high-grade PIN carefully
and may advise a repeat prostate biopsy, especially if the original
biopsy did not take samples from all parts of the prostate.
Another finding that may be reported on a prostate biopsy is atypical small acinar
proliferation (ASAP), which is sometimes just called atypia. In ASAP,
the cells look like they might be cancerous when viewed under the
microscope, but there are too few of them on the slide to be sure. If
ASAP is found, there's about a 40% to 50% chance that cancer is also
present in the prostate. This is why many doctors advise getting a
repeat biopsy within a few months.
Another finding that may be reported on a prostate biopsy is proliferative inflammatory
atrophy (PIA). In PIA, the cells look abnormal when viewed
under the microscope. Although PIA is not cancer, researchers believe
that some PIA cells can turn into prostate cancer directly or by first
changing into high-grade PIN.
Last Medical Review: 10/29/2008
Last Revised: 08/25/2008
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