The Causes of Prostate Cancer


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 regular check-ups 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 check-ups 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 their nineties.

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 recent 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 is true 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 prostate cancer!

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 of prostate 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 watchful waiting rather than attempting curative therapy. You and your doctor need to make decisions like this together, and you should ask your doctor for all the information he or she can give you before you take those decisions.




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