Prostate-specific antigen (PSA) is a protein produced in the prostate gland. Small amounts of PSA are normally found in men’s blood. The PSA blood test is used to screen for prostate cancer, because the greater the level of PSA is in the blood, the more likely it is that cancer is present. However, the PSA test does not distinguish between prostate cancer and noncancerous factors that may affect the PSA level. Only a biopsy can diagnose prostate cancer.
What PSA Levels Indicate
PSA levels are measured in nanograms per millilitre (ng/ml). According to the National Cancer Institute, while higher PSA levels are correlated to a greater incidence of prostate cancer, there is no absolute normal or abnormal PSA level. About 15 per cent of men with PSA levels under 4 ng/ml will have prostate cancer. For levels from 4 to 10 ng/ml, there is a 20 to 30 per cent risk of prostate cancer. Between 10 and 20 ng/ml, the risk is 50 to 75 per cent, and it rises to 90 per cent when PSA levels go above 20 ng/mL.
What Affects PSA Levels
While prostate cancer usually raises the PSA level found in blood, other factors can do so as well. PSA levels normally rise with age. Benign prostatic hyperplasia (BPH), a noncancerous enlargement of the prostate common in older men, causes higher PSA levels; the larger the prostate is, the higher the PSA is. Infections or inflammations of the prostate gland will raise PSA levels.
Other factors may cause PSA levels to be low, even when cancer exists. They include certain medications, herbal supplements targeted at prostate health and ejaculation within two days of testing.
Who Is At Highest Risk For Prostate Cancer
According to the American Cancer Society, risk factors for prostate cancer include age, race, location and family history. • Age is the greatest risk factor. Two-thirds of all cases of prostate cancer occur in men age 65 or older.
• African-American men are at greater risk for prostate cancer than other races and are more likely to be diagnosed at an advanced stage. Asian-American and Latino men have the lowest rates of prostate cancer.
• Prostate cancer is more common in North America, Australia, parts of Europe and the Caribbean, and less common in Asia, Africa, Central America and South America.
• Having a father or brother with the disease doubles the risk. Three or more relatives with prostate cancer, or relatives diagnosed younger than age 55, further increases the risk.
• A diet rich in red meat or high-fat dairy products and low in fruits and vegetables may also be linked to a higher incidence of prostate cancer, although this is still being studied.
Pros and Cons of the PSA Test
There is controversy regarding whether the benefits of screening outweigh the risks and pain of follow-up diagnostic tests and treatment.
The most positive aspect of the PSA test is that it can detect cancer at an early stage, when it can most easily be cured. But it is not 100 per cent accurate. It does not distinguish between prostate cancer and noncancerous tumours, or other factors that may raise PSA levels. It results in both false-positives (when cancer is not present) and false-negatives (overlooking the presence of cancer.) False-positives cause stress and worry, and many men undergo biopsies, with side effects that may include pain, infection and bleeding. False-negatives mean that some cases of prostate cancer will be missed.
In addition, the PSA test cannot determine how aggressive a case of prostate cancer can be. Some cases of prostate cancer grow so slowly that they may never cause symptoms or problems over the course of a man’s life. Early detection of these slow-growing cancers may result in treatments such as surgery or radiation with side effects that may seriously affect the quality of life.
For this reason, the American Cancer Society strongly recommends that men make decisions about screening based on available information as well as discussions with their doctors.
In 2008, the U.S. Preventive Services Task Force recommended against routine screening for men aged 75 or older, because they will probably die from other causes before succumbing to a slowly progressing prostate cancer.
Statistics About Prostate Cancer
After skin cancer, prostate cancer is the most common cancer to affect American men, responsible for about 10 per cent of cancer-related male deaths.
The American Cancer Society estimated about 192,280 new cases of prostate cancer in 2009, and 27,360 deaths.