The Causes of Prostate Cancer
Last Revised April 8, 1998.
The importance of genetics |
The significance of race |
The age factor |
What about diet and the environment? |
Is prostate cancer related to vasectomy? |
Are all cases of prostate cancer equal in risk?
Put in the simplest way, no one knows what causes some men to get
prostate cancer while other men don't. Scientists and clinical
researchers are working very hard to try to discover the answer to this
very basic question. We hope they will find the answer soon. In the
meantime, here are most of the things we do know.
The recognized risk factors for prostate cancer (i.e., things that make it more
likely that a particular man may get this disease) include age, race or
genetics, and environment. Approximately 184,500 American men are
expected to be diagnosed with prostate cancer in 1998. This is compared
to 165,000 in 1993. In other words, the incidence of prostate cancer
appears to have been rising slowly ... but in fact it rose rapidly from
1993 to 1996 and then fell again.
Also in 1998, the number of American men who are predicted to die
of prostate cancer is predicted to be 39,200. Approximately 3% of all
deaths of American men are currently believed to be caused by prostate
cancer. This is a large number of people, but it means that only three
men in 100 will actually die of the disease.
The American Cancer Society (ACS) is, in fact, for 1998, projecting a decline in new
cases of prostate cancer and in prostate cancer deaths. This is the first
time we have ever seen a projected decline in these numbers at the time the ACS
issues its annual projections.
The fact that more
American men will be found to have prostate cancer in 1998 compared to
1993 is not necessarily because more men are getting
prostate cancer. It is in fact much more likely that we have become
better at finding prostate cancer. At the beginning of 1997,
it was projected that over 330,000 men would be diagnosed with prostate cancer
in that year. That figure had to be significantly revised downward
as new data became available. However, men are
living longer than they used to, so their chances of
living long enough to get prostate cancer are increased.
The importance of genetics
If your brother or your father or your uncle
has or had prostate cancer, then there is an increased chance that you
will have prostate cancer. In other words, for many men the risk of
prostate cancer is associated with a family history of the disease.
However, this does not mean that just because your father had prostate
cancer you will get prostate cancer! It does mean that the more
relatives you have who had or have prostate cancer, the greater is your
risk. This is important and affects when a man should start to have
for signs of prostate cancer.
As with other diseases,
scientists and other researchers are racing each other to find genes
which are common to individuals with prostate cancer. In a variety of
cancers (breast cancer, renal cell carcinoma, and others) genes have
now been found which are specifically related to these cancers in some
families with a very high incidence of that particular disease. Some
genes have also been identified that may be significant in the development of
certain types of prostate cancer. However, these genes are just one step
on the way to greater knowledge.
Their discovery and isolation will not immediately lead to genetic tests
for prostate cancer in most individuals, let alone to some form of
universal cure for this disease.
You are likely to hear more and more
about the genetics of prostate cancer in years to come, along with
references to genes like p53, Her-2, neu, and others,
most of which will
have minimal actual impact on your personal situation.
The significance of race
Prostate cancer is much more common in some
races than in others. For example, Japanese men living in Japan have
an extremely low incidence of prostate cancer. By comparison African
American men are at very high risk of this disease. Why is this? We
don't know. What we do know is that it isn't just about their genetics
and heritage, because men of Japanese origin living in America have a
similar risk of prostate cancer as any other average American man living
in the same area! However, race can be an important factor in
determining when a man should begin to have regular
for signs of prostate cancer.
The age factor
As you grow older, your chance of having a diagnosis of prostate cancer
increases. In fact, we believe that one
of the reasons that prostate cancer is now so much more common than it
was 50 years ago is very obvious: more men live longer today than they
did 50 years ago. If you live longer, your chance of having a
diagnosis of prostate cancer goes up proportionally.
The average age of men diagnosed with prostate cancer in America is still
over 60 years (although diagnosis in younger men is much more common than
it used to be). And the range of ages is very wide. Cases of prostate
cancer have first been seen in men in their twenties and in men in
What about diet and the environment?
There is a great deal of circumstantial evidence that appears to support
the idea that diet is important in the avoidance of prostate cancer. On the
other hand, despite a great deal of effort to prove connections between
diet and prostate cancer, we have totally failed to do this. One relatively
major study has clearly linked prostate cancer risk with
saturated fat intake. The most
likely situation is that a good, well balanced diet which is high in
fruit and vegetables and relatively low in red meat and fats will be
better for you than a diet that is high in red meat and fats. This is
true generally, and has nothing especially to do with prostate cancer!
Eating well is good for you! There is no known diet that will prevent
prostate cancer -- and there probably never will be!
Roughly the same is true of the environment. The cleaner your environment
the less likely you are to be at risk of prostate cancer. But then that
for nearly all cancers, and explains why smoking is such a particularly
foolish thing to do if you want to avoid cancer. Smoking introduces
pollutants directly into your lungs, and from there to almost every
other organ of the body. You might as well go and stand beside the
nearest major freeway and inhale car and truck exhaust fumes all day!
Once again, however, there is no perfectly clean environment that will
allow you to live without the risk of prostate cancer!
Having said that, why is it that when Asian males move from Asia
to America their risk of prostate cancer rises so rapidly? Is it the
change in diet?
Is it the change in the environment? Is it just that they are more
likely to get tested for prostate cancer in America than they were in
Asia? What is going on? Unfortunately, we don't know.
Is prostate cancer related to vasectomy?
One question that crops up over and over again is whether having a vasectomy
(the procedure that stops a man from making a woman pregnant) can lead to
a later diagnosis of prostate cancer.
First of all, it has to be said that men who have vasectomies do appear
to be more likely to have a diagnosis of prostate cancer 20 years later than men who do
not have vasectomies. However, it also has to be said that there is absolutely
no evidence whatsoever of a cause and effect relationship. Indeed, there is
good reason to believe that this is a statistical coincidence that has to do
with the attitudes to health of men most likely to have vasectomies.
Basically, men who have vasectomies exhibit what is widely described as
"health-seeking" behavior. In other words, they are the type of men who
look after their health, tend to go for regular check-ups, and generally
have a lifestyle which could be considered as "healthy." They are presumed
to be more likely to have vasectomies because they have considered that
the risks associated with a vasectomy are far lower than the risks associated
with their wife/partner having a late or unwanted pregnancy.
Now it is also reasonable to suppose that men who exhibit health-seeking
behavior are more likely to seek regular prostate examinations as part of
that behavior. This immediately implies that the same men who seek vasectomies
are more likely to have a prostate examination than the men who do not have
vasectomies. Therefore these men are more likely to be diagnosed with
The bottom line is that men who have vasectomies are somewhere between
1.5 and 2.0 times more likely to have a later diagnosis of prostate cancer
than men who have not had a vasectomy ... but that we have no reason to believe
that there is any connection between the two.
Are all cases of prostate cancer equal in risk?
Bluntly, no they aren't. One of the most infuriating problems is that
for many men a diagnosis of prostate
cancer is not significant! If you look at the prostates taken from
100 American men over 50 years old who die in car crashes and similar
accidents, that is men who never showed any clinical sign of prostate
cancer while they were alive, you can, in fact, find small areas of
cancer in the prostates of about 30 of those men (30%). Those men
could have lived for years with those small areas (foci) of prostate
cancer -- or some of them could have been diagnosed with clinically
significant prostate cancer just a few months later if they had lived.
If you do the same thing with American men over 90 years old, you find
that 90% of them have microscopic evidence of prostate cancer.
These small areas of prostate cancer tissue that do not develop into
clinically important disease are often called "latent" prostate cancer.
For an average American man of 50 years of age, with a reasonable life
expectancy of another 25 years, the chance that he will develop a
microscopic focus of so-called "latent" prostate cancer tissue is
estimated to be 42% (that is, 42 of 100 such men will get such a
microscopic focus). However, the chance that the same man will get
clinically significant prostate cancer (that is, prostate cancer that
is associated with clear signs or symptoms of the disease) is only
9.5%. Finally, of the same 100 men, only about three will actually die
of prostate cancer. So you can clearly see that while many men may get
prostate cancer, it will actually affect relatively few of them very
seriously. It is often said that most men are much more likely to die
with prostate cancer than because of this disease.
We do not yet know how to tell which men with a small focus of prostate
cancer are most likely to go on to get clinically significant disease.
This is one
of the most important things to understand about prostate cancer. It
affects almost everything about the disease. It is something you should
think about and
discuss with your doctor before you ask to have specific tests
for prostate cancer
and most certainly before you receive treatment for early stages
cancer which are confined to the prostate. You may be better off
not having the specific tests if you have absolutely no reason to
believe you are at risk for prostate cancer. And even if you are
diagnosed with a small focus of cancer confined to the prostate, you may
be better off if the doctor practices so-called
rather than attempting curative therapy. You and your doctor
need to make decisions like this
and you should ask your doctor for all the information he or she can give
you before you take those decisions.