Problems with the PSA

taken from Small Gland, Big Problem 4th Edition
by Professor Roger Kirby, Health Press 2011

Overdetection of clinically insignificant cancers

As prostate cancer occurs mainly in men beyond middle age, it is perfectly possible that a small cancer might never grow sufficiently large to cause problems during a man’s lifetime. The anxiety caused by a ‘positive’ (high) PSA result might reduce the man’s quality of life by causing unnecessary worry, whereas if he remained ignorant of his condition, his life would be unaffected. However, fears of this sort of overdiagnosis and overtreatment of prostate cancer have lessened as doctors increasingly use ‘active surveillance’ as a treatment strategy for smaller low-risk cancers.

‘False-positive’ results

An elevated level of PSA in the blood does not necessarily indicate cancer. Indeed, the average PSA level rises with age and any disease of the prostate – particularly BPH, but also prostatitis – can result in an elevated PSA.

A high PSA value, or one that increases over time, may prompt a doctor to request a biopsy, which involves taking samples of tissue from the prostate. However, scientific studies have shown that when samples of prostate tissue are examined under the microscope, only one man among four with a PSA value between 4 and 10 ng/mL will be found to have cancer (so three of the four will not have cancer even though their PSA levels are raised).

Using a higher cut-off value (say PSA above 10 ng/mL), the probability that a subsequent biopsy will confirm prostate cancer rises to more than 60%. Of course, the problem with using a higher cut-off to determine who should undergo a biopsy is that as the cut-off value increases, so does the ‘false-negative’ rate. (A false-negative result is a PSA test result below the cut-off value, but the man has prostate cancer; this is illustrated in the diagram on page 16. Remember that early prostate cancer can be present even when the PSA value is below 4 ng/mL.) Also, if cancer is to be identified at a stage when it is still curable, then it should be detected before the PSA rises much above 10 ng/mL.

There has been great interest in measuring the rate of PSA change over time. Although the information on this subject is only provisional, as already mentioned, it seems that men whose PSA rises by more than 0.75 ng/mL per year are at higher risk of harbouring the more aggressive form of prostate cancer as opposed to a less aggressive type of tumour, which in fact carries little risk of spread (an analogy is to liken the aggressive tumours to ‘tigers’, while the more innocuous tumours are more comparable with ‘pussy-cats’). In order to detect the rate of PSA change, regular (usually yearly) blood tests are required. These can usefully be combined with cholesterol, lipid and blood sugar measurements, provided that fasting blood samples are obtained.

Anxiety before the results become available

The speed with which you get your test results depends on where you have your test. It can take anything from a couple of hours to several weeks – obviously those waiting at the longer end of the scale have more time to become anxious. Ask your doctor about the usual waiting time for results. Bear in mind, however, that minor fluctuations are common. Ask your doctor to explain any variations.

Over-the-counter PSA tests, which will allow self-testing, are available in chemist shops. Like the whole PSA issue, these home tests are rather controversial.

The pros and cons of PSA testing
Pros Cons
  • Allows early detection of potentially curable prostate cancer
  • Permits the doctor to estimate prostate size in a patient with BPH
  • Helps the doctor predict response to certain drugs
  • Allows the doctor to estimate how advanced the cancer is at diagnosis
  • Can be used to monitor men at increased risk of prostate cancer, such as those with a family history
  • Can help the doctor estimate the patient’s risk of developing prostate cancer in the future
  • A negative result is reassuring
  • Sequential values provide extra information about cancer risk
  • Helpful for monitoring response to treatment
  • Clinically insignificant cancers may be detected causing needless worry and further medical procedures for the patient
  • Men without cancer may have a false-positive result (particularly those with borderline PSA values)
  • A false-negative result may provide unwarranted reassurance
  • There are cost implications – not only regarding the PSA test, but of biopsy and treatment options if the biopsy is positive
  • Those undergoing biopsy are exposed to the risks of bleeding and infection
blood test
An ‘ideal’ blood test for prostate cancer should clearly distinguish men who have cancer from those who do not. Although PSA measurement is a useful test, it is not perfect – if a cut-off of 4 ng/mL is used, there is an overlap between patients with BPH or other diseases and those with prostate cancer. Inevitably, this results in some men worrying unnecessarily that they may have cancer