The Prostate Specific Antigen (PSA) test is widely available and is able to detect many prostate cancers in men who have no outward symptoms. There are benefits and risks associated with catching prostate cancer at an early stage, however, and men should consider these carefully before deciding whether or not to have the test.
Medical opinion is divided: Some experts argue that all men over 50 years should be tested annually, while others believe that there is a lack of evidence to support such a recommendation. It has not yet been proved that routine PSA testing saves lives, and the controversy will continue to rage until the results of large clinical trials become known in around 10 years time. Until then, a suggested approach is to offer PSA testing on an individual basis to men aged 50–75 years with a life expectancy of at least 10 years, and to make them fully aware of the limitations of testing and available treatments.
Prostate Cancer
Prostate cancer is a common malignancy that affects around 1 in 10 men in western nations and is a major cause of cancer deaths. It is an uncontrolled growth of cells in the prostate gland, a male sex gland that lies below the bladder. Most cases are detected in men over the age of 50years, with more than 80% of all cases being diagnosed in men over the age of 65 years. Not all prostate cancers are the same: Some tumours are slow-growing and never cause any symptoms, while others are fast-growing and can spread to other parts of the body.
The PSA test
The PSA test was introduced in the late 1980s to help detect prostate cancer in its early stages, before the tumour has grown large enough to cause symptoms. Produced by the prostate gland, PSA can be detected in the blood, and raised levels may indicate a problem. Raised PSA levels do not necessarily mean cancer, however: PSA levels are also elevated in men with inflammation of the prostate gland (“prostatitis”) or an enlarged but non-cancerous prostate (“benign prostatic hyperplasia”).
Divided opinion
Although it has been around for more than 15 years, the PSA test is still surrounded by controversy. While there is no doubt that it can help detect prostate cancer at an early stage, medical experts disagree over whether it should be used as a screening test. Some medical organisations recommend that all men should undergo yearly PSA testing from age 50 years onwards. They also suggest that men at high risk of prostate cancer – such as black men and those with a family history of the cancer – should start PSA screening at age 40. Other organisations advise doctors to provide their patients with information about prostate cancer and explain the pros and cons of PSA testing, to allow the man to make his own informed decision.
What is screening?
The purpose of screening is to identify disease in symptom-free people at a stage when treatment will alter the natural course of the condition. In 1968, scientists at the World Health Organisation developed ten principles that should guide a national screening program. These are: - The condition is an important health problem
- Its natural history is well understood
- It is recognisable at an early stage
- Treatment is better at an early stage
- A suitable test exists
- An acceptable test exists
- Adequate facilities exist to cope with abnormalities detected
- Screening is done at repeated intervals when the onset of the disease is insidious
- The chance of harm is less than the chance of benefit
- The cost is balanced against benefit
To date, prostate cancer screening fulfils few of these conditions. A major argument against screening is the lack of evidence that PSA testing has reduced deaths from prostate cancer or improved the lives of men diagnosed with the condition.
Statistics show that deaths from prostate cancer have been falling since around 1990, and some have interpreted this as being due to earlier detection of tumours through the PSA test. But this link has not been proven – it is just one interpretation of the figures. Indeed, it has been calculated that screening would take 10–15 years to have an impact on death rates – suggesting PSA screening cannot take the credit.
Need for randomised controlled trials
The “gold standard” for assessing the impact of any intervention on a disease is a randomized controlled trial, and no such trials have yet been completed for PSA testing in prostate cancer. Two studies are underway in the United States and Europe and should provide important new information about the benefits and risks of screening. In these studies, which involve more than 300,000 healthy men, half will undergo yearly PSA testing while the other half will only be tested if they develop symptoms. Results are due in around 10 years and will reveal whether PSA testing does indeed save lives. In the meantime, men must carefully weigh up the pros and cons of having a PSA test. Some of the issues to be considered are listed below:
Pros: - PSA testing is quick and simple, involving just a blood test
- Regular PSA testing can find prostate cancer long before symptoms appear; the test catches four out of five cancers in the early stages
- Prostate cancer is much easier to treat and cure if it is found early, before the tumour has spread to other parts of the body
- PSA testing may save lives by detecting aggressive tumours at an early stage, although this has not yet been proven
Cons: - As with other medical tests, men (and their families) may feel very anxious while waiting for the results
- The PSA test is not a test for prostate cancer – it simply indicates a problem with the prostate gland, and most men with a positive PSA test do not have cancer
- A positive PSA test can therefore lead to additional medical investigations (which also have risks), unnecessary worry, and financial costs
- The PSA test is not 100% accurate: One in five men with early prostate cancer will have a negative PSA test, leading to a false sense of security
- PSA testing may lead to the treatment of a cancer that would never have caused any health problems; treatment is associated with side effects such as incontinence and impotence that can reduce general wellbeing and quality of life
- Treating prostate cancer in men over the age of 75 years or those with other serious health problems is unlikely to lengthen lifespan
- Experts have not yet proved that PSA testing reduces prostate cancer deaths
Further information:
American Cancer Society
www.cancer.org
American Urological Association
www.auanet.org/
Cancer Research UK
www.cancerresearchuk.org
CancerBACUP
www.cancerbacup.org.uk
Centers for Disease Control and Prevention
http://www.cdc.gov/ National Comprehensive Cancer Network
http://www.nccn.org/
US National Cancer Institute
http://www.nci.nih.gov/
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