PSA: to test or not to test?
When the Ontario government tabled its 2008 budget, it set aside money to pay for a test that helps in the early diagnosis of prostate cancer. Ontario becomes the seventh province to pay for the prostate-specific antigen (PSA) test. Quebec, Alberta and British Columbia are the only jurisdictions in the country that require patients to cover the cost themselves.
The Prostate Cancer Research Foundation of Canada called the decision a step in the right direction and urged the other three provinces to follow Ontario's example.
More men will be diagnosed with prostate cancer in 2008 than women will be diagnosed with breast cancer, according to figures released by the Canadian Cancer Society. It is, by far, the most common cancer in men. Among cancers, it is the third leading cause of death, after lung cancer and colorectal cancer.
The lifetime risk for a man of being diagnosed with prostate cancer is 12.3 per cent. The lifetime risk of dying from the disease is 3.8 per cent.
What is prostate-specific antigen?
PSA is a protein produced by your prostate — whether or not it contains cancerous cells. Its job is to help liquefy semen. The rate at which PSA enters the bloodstream depends upon the health of the prostate. Cancer cells generally make more PSA than do normal cells, leading to higher levels of PSA in the blood in the early stages of prostate cancer.
What does the PSA test do?
It measures the level of PSA in your bloodstream.
Does a positive PSA test mean I have prostate cancer?
Not necessarily. Conditions besides prostate cancer can lead to higher than normal PSA levels, including enlargement of the prostate (which is not uncommon as men age) and inflammation of the prostate (prostatitis). There are other factors to consider when interpreting the results of your PSA test:
- Your age.
- The size of your prostate.
- How quickly your PSA levels are changing.
PSA tests can't distinguish between prostate cancer and other non-cancerous prostate conditions like prostatitis and enlargement of the prostate.
Who should get PSA tests?
Prostate cancer normally affects older men. More than 75 per cent of men diagnosed with the disease are over 65. But it can hit men who are still in their 40s.
Besides age, family history, diet and ethnicity may also play a role in your risk of developing prostate cancer. Research suggests that prostate cancer may be more common in black men than in white men and less common in Asian and aboriginal men.
If your brother or father was diagnosed with the disease, your risk may be higher. A high-fat diet may also increase your risk.
The Canadian Cancer Society suggests men over 50 should talk to their doctor about getting tested for prostate cancer. It also suggests that if you are over 40 and have a higher risk of developing the disease, you should talk to your doctor about getting tested.
But for healthy men with no symptoms of the disease, the society notes, there are no recommended screening tests.
The Canadian Task Force on Preventive Health Care recommends against PSA screening while the World Health Organization concludes that it's not clear whether screening reduces the number of deaths from the disease.
An editorial in the Canadian Medical Association Journal in August 2004 was titled "Pound of Prevention, Ounce of Cure?" It questioned whether there was any benefit in aggressively treating a person who may be years away from showing any symptoms.
While a PSA test may help detect cancer early, it may detect a cancer that is slow-growing and may never be a threat to your health.
What does the research say about PSA tests?
Most research shows that PSA tests are effective in diagnosing disease in men who are at higher risk or are showing symptoms of prostate cancer.
But the test also has a high rate of false-positive results — suggesting cancer when none is present. That can lead to invasive followup tests in a healthy man.
Most research has been unable to establish a link between declining death rates from prostate cancer and widespread screening for the disease.
Another study cited in the CMAJ (June 19, 2007) suggested that doctors should stop using the terms "normal" and "elevated" as descriptors of PSA test results. The researchers argued that PSA levels vary greatly from person to person and are just one factor in determining cancer risk.
Two large international studies of 257,000 men published March 18, 2009, in the New England Journal of Medicine found that the benefits from a PSA test were fairly small and the risks in terms of unnecessary treatments were quite large.