Prostate Cancer: to Screen or Not to Screen

One of the areas in which our medical practice aims to excel is in screening and prevention.

Having a computer system as sophisticated as ours and having a large team of Practice Nurses makes us uniquely suited to screening for preventable diseases.  The Practice Nurses will be actively inviting and recalling patients for screening tests and health advice each year.

So it has come as a bit of a shock to some of our male patients to find that we are not routinely screening for prostate cancer.  So much so, that I thought it would be a good idea to look at the pros and cons of screening in general, and the specific problems with prostate screening.

The perfect screening test will be (1) safe, and (2) reliable and will look for a disease that is (1) serious and (2) is either preventable or treatable.

Unfortunately, there is no such screening test in existence.  Let's take prostate cancer.  The test itself (called the PSA test) is safe - it's just a blood test - but it is very far from reliable.  Having a high PSA does not mean you have cancer, and having a low PSA does not mean you do not have cancer. 

Then there is the question of how serious prostate cancer is.  Everyone is afraid of the 'C' word, so anything that is cancer must always be bad.  Not so.  The great majority of men who get prostate cancer will not suffer any real harm from it.  However, a small number of men with prostate cancer will die from it.  It's not possible to tell the 'indolent' cancer from the dangerous one.

This means that you have to 'treat' a lot of men who have nothing serious wrong with them in order to catch the small number who do have a serious cancer.  And the treatment is not safe and simple - it is a biopsy or an operation can lead to incontinence and sexual dysfunction.

In fact, to treat a single man with a serious cancer you have to screen around 1,400 men and you will end up 'treating' around 48 men who had nothing serious wrong with them.  So only around 2% of men who think they have had treatment for prostate cancer actually had serious prostate cancer.  The other 98% had nothing serious wrong with them.  Except, now they think they have a cancer.  Worse, we will likely never know which patient is which.

Patient's don't believe me when I tell them that the evidence is that if you have a PSA test your chances of being harmed can go up.  ("Just from a blood test!?  Are you sure you're a real doctor?")

Ironically, this is because of what is called the Popularity Paradox.  This is what happens:

1. A healthy 45 year old man with nothing wrong with him takes a PSA test.
2. The PSA comes back falsely high.
3. The man (and his doctor) think he has prostate cancer because of the high PSA.
4. The man has a biopsy, which is inconclusive.
5. The man has prostate surgery which results in life-long incontinence and impotence.
6. The man thinks his life has been saved by the surgery and tells all his friends and relatives that they must have the test too.

That's an extreme example, but you get the idea.  (It should be noted, that the great majority of men diagnosed with prostate cancer don't need treatment.)

In other words, the more harm you do the more the patient thinks you have helped them.  The Popularity Paradox that is the bane of evidence based screening.

Worse still, the side effects of treatment are all 'front-loaded' - they happen at the time of treatment - but the possible benefits (if any) are all 'tail-loaded' - they don't happen for decades (if ever).

And yet, prostate cancer kills over 4,000 men a year in Canada (around 11% of all cancer deaths in men).

So this gives us a real dilemma.  If the evidence is that your chances of being harmed go up or stay the same when you get a PSA test, then should we be doing PSA's at all?

Well, that depends on a lot of things.  Do you have a family history of prostate cancer (in a first degree relative at a young age)?  Do you have symptoms?  (Our nurses will give you a questionnaire to fill out.)  What are you more afraid of personally?  What is your attitude towards risk?

That's why we won't be performing routine PSA screening at present.   As recommended by Health Canada, the NHS in the UK, and the US Preventive Task Force We'll want to go over the risks and benefits with each patient carefully before they decide whether to have the test or not.


Research continues in this area, and as any fresh information comes to light we will review our advice.


Links:
Health Canada Prostate Cancer page

New England Journal of Medicine Perspective Roundtable: Screening for Prostate Cancer


(Any patient interested in prostate screening should call to make an appointment with one of our Practice Nurses to discuss the test.)