Prostate Screening

It will come as no surprise to many that one of the most common conditions that men ask about screening for is prostate cancer.

Prostate cancer is relatively common and is increasingly likely to affect men as they get older.

Fortunately, because the prostate gland is wrapped around the urethra (the tube that takes urine from the bladder to the outside) prostate cancer often causes early symptoms which men can detect.

Although these symptoms also indicate harmless disease, we advise ALL men with ANY of these symptoms to speak to a doctor quickly.

Hesitancy - taking a little longer than usual to start passing urine.
Poor Stream - the flow of urine is not as strong as it once was.
Dribbling - persistent dribbles after the main flow of urine has ended.
Getting up at night to pass urine - getting up at night has many causes - if prostate related, usually there are other symptoms too.
Blood in the urine or semen - this is not just for prostate cancer. Blood in the urine is NEVER normal and ALWAYS needs investigation.

For men who have these symptoms, a rectal examination and a PSA (prostate specific antigen) blood test are useful to assist in ruling out prostate cancer.

The difficulty arises when we try to use PSA to screen men who have no symptoms but who would like to have the condition excluded.

Sadly, the test cannot tell for certain whether a cancer is present or not. Neither can it tell whether any cancer detected is aggressive and likely to require treatment, or relatively harmless and unlikely to cause a problem. In order to improve the test, research has been undertaken which has identified the PSA levels in many men of all ages who have prostate cancer and we set our upper limit of normal according to age, with the intention of detecting 95% of all men with prostate cancer. Unfortunately, 15% (or about 1 in 8) of men who do not have prostate cancer will also have PSA levels above this nominal upper level of normal.

The difficulty mentioned above occurs because there is a reasonably wide range of PSA test results found in both health men and those affected by prostate cancer. There is a substantial overlap between the test results of healthy men who happen to have a slightly higher than average PSA and men with cancer who have no significant rise in their PSA levels. This issue is not unique to PSA - it is a problem with many tests for many conditions.

If you are confused after reading this, YOU ARE NOT ALONE! Please discuss this with your doctor.

In order to understand whether PSA screening is useful or not, it is most helpful to discuss an example. When examples are used, it is only right that we should explain why we chose the example we did. In this case, we illustrate a sample of men who are in the age group most likely to ask about PSA screening. For the age goup 55 to 64, US statistics for white and hispanic males (who have similar risks) suggest that close to 1 in 200 men will have prostate cancer. NOTE: the risk for men of African origin is MUCH higher and these statistics do not apply to this one racial group.

Consider therefore, 200 men without symptoms who choose to undergo PSA testing

30 men will have positive tests. (one eighth of 200)

All 30 will have to undergo further investigation including ultrasound testing, further blood testing and possibly prostate biopsy. Prostate biopsy has an 85% rate of significant complications (mainly pain and bleeding of short duration) but is associated with severe infection in a few cases and also, rarely, death. Even a prostate biopsy can miss prostate cancer (about 10%) and so the tests may have to be repeated after a while, just to be on the safe side.

1 man has prostate cancer. The PSA test has a 1 in 20 chance of missing this man and giving him a 'normal' result. There is no way to be sure that this man is included in the 30 with positive tests.

Because of the low risk of prostate cancer (1 in 200) in men aged 55 to 64 and the fact that you are 30 times more likely to have a positive test than you are to have prostate cancer, we DO NOT recommend routine PSA testing for men with no symptoms of prostate cancer.

That having been said... There have been two recent trials looking into whether PSA screening has survival benefits. These have at best been inconclusive, showing either no benefit or minimal benefit though it would appear that at least there is no evidence it does serious harm. There may yet be a place for PSA screening and there remains some interesting work yet to be done on the subject.

Further information is available on the NZ Guidelines Group website. Just search for prostate from the home page. The NZGG statistics are much more pessimistic than ours as they include all men rather than the higher risk group we chose to illustrate.

It's YOUR decision...

We recognise that interpretation of risk is a very personal decision and not one we can make for you.

We recommend that you discuss testing with your doctor and with trusted friends.

If, having reviewed the evidence, you decide that you would like to have PSA testing performed, we shall be pleased to help you to arrange it.

On the Horizon....

There is substantial debate about the value of serial PSA results. To date there is insufficient evidence to suggest that monitoring PSA regularly is better than taking a single test but common sense suggests that if we have enough test results for one individual, we can determine a normal level for that person and also detect changes more easily. Sadly, it will require more study to determine the value, or otherwise of this supposition.

There is a new test currently undergoing clinical trials which has promise. This test, if it can pass the rigours of scientific analysis, may well offer the real screening test men desire.

Factual notes:

The 1 in 200 incidence of prostate cancer is taken from US statistics for the last 10 years. The incidence for black males is nearly double that for other races.

The 95% range is usual for almost all blood tests. The test is performed on many apparently healthy individuals and statistical analysis determines the upper and lower limits of normal needed to include 95% of these people.

The complication rate quoted for prostate biopsy is from a well conducted study from Turkey: Urol Int 2004;72:303-307