Prostate-specific antigen, or PSA, is a chemical produced by the prostate gland. PSA functions to liquefy semen following ejaculation, aiding the transit of sperm to the egg. A small amount of PSA filters from the prostate into the blood circulation and can be measured by a simple blood test. In general, the larger the prostate size, the higher the PSA level, since larger prostates produce more PSA. As a man ages, his PSA rises based upon the typical enlarging prostate that occurs with growing older.
How is PSA used to screen for prostate cancer?
Using PSA testing, about 90% of men have a normal PSA. Of the 10% of men with an elevated PSA, about 30% will have prostate cancer. In a recent study of 350,000 men with an average age of 55, median PSA was 1.0. Those with a PSA greater than 1.5 had a 0.5% risk of developing prostate cancer, those between 1.5-4.0 had about an 8% risk, and those greater than 4.0 had more than a 10% risk.
Although it is an imperfect screening test, PSA remains the best tool currently available for detecting prostate cancer. It should not be thought of as a stand-alone test, but rather as part of a comprehensive approach to early prostate cancer detection. Baseline PSA testing for men in their 40s is useful for predicting the future potential for prostate cancer. The most informative use of PSA screening is when it is obtained serially, with comparison on a year-to-year basis providing much more meaningful information than a single, out-of-context PSA.
Is there any truth that the PSA test is worthless?
A major backlash against screening occurred a few years ago with the United States Preventive Services Task Force (USPSTF) grade “D” recommendation against PSA screening and their call for total abandonment of the test. This organization counseled against the use of PSA testing in healthy men, postulating that the test does not save lives and leads to more tests and treatments that needlessly cause pain, incontinence and erectile dysfunction. Please note, there was not a single urologist on the committee. The same organization had previously advised that women in their 40s not undergo routine mammography, setting off another blaze of controversy. Uncertainty in the lay press prompted both patients and physicians to question PSA testing and recommendations for prostate biopsy.
Is there really any harm in screening? Although there are potential side effects from prostate biopsy (although they are few and far between) and there certainly are potential side effects with treatment, there are no side effects from drawing a small amount of blood. The bottom line is that when interpreted appropriately, the PSA test provides valuable information in the diagnosis, pre-treatment staging, risk assessment and monitoring of prostate cancer patients. Dismissing this important test does a great disservice to patients who may benefit from early prostate cancer detection.
Why should I get screened for prostate cancer?
Excluding skin cancer, prostate cancer is the most common cancer in men (1 in 9 lifetime risk), accounting for one-quarter of newly diagnosed cancers in males. Prostate cancer causes absolutely no symptoms in its earliest stages and the diagnosis is made by prostate biopsy done on the basis of abnormalities in PSA levels and/or digital rectal examination. An elevated or accelerated PSA that leads to prostate biopsy and a cancer diagnosis most often detects prostate cancer in its earliest and most curable stage. Early and timely intervention for those men with aggressive cancer results in high cure rates and avoids the potential for cancer progression and consequences that include painful cancer spread and death.
The upside of screening is the detection of potentially aggressive prostate cancers that can be treated and cured. The downside is the over-detection of unaggressive prostate cancers that may never prove to be problematic, but may result in unnecessary treatment with adverse consequences. The downside of not screening is the under-detection of aggressive prostate cancers, with adverse consequences from necessary treatment not being given.
Why is PSA elevated in the presence of prostate cancer?
Prostate cancer cells do not make more PSA than normal prostate cells. The elevated PSA occurs because of a disruption of the cellular structure of the prostate cells. The loss of this structural barrier allows accelerated seepage of PSA from the prostate into the blood circulation.
Does an elevated PSA always mean one has prostate cancer?
Not all PSA elevations imply the presence of prostate cancer. PSA is prostate organ-specific but not prostate cancer-specific. Other processes aside from cancer can cause enhanced seepage of PSA from disrupted prostate cells. These include prostatitis (inflammation of the prostate), benign prostatic hyperplasia (BPH, an enlargement of the prostate gland), prostate manipulation (e.g., a vigorous prostate examination, prostate biopsy, prolonged bike ride, ejaculation, etc.).
Why is PSA an imperfect screening test?
PSA screening is imperfect because of false negatives (presence of prostate cancer in men with low PSA) and false positives (absence of prostate cancer in men with high PSA). Despite its limitations, PSA testing has substantially reduced both the incidence of metastatic disease and the death rate from prostate cancer.
Who should be screened for prostate cancer?
Men age 40 and older who have a life expectancy of 10 years or greater are excellent candidates for PSA screening. Most urologists do not believe in screening or treating men who have a life expectancy of less than 10 years. This is because prostate cancer rarely causes death in the first decade after diagnosis and other competing medical issues often will do so before the prostate cancer has a chance to. Prostate cancer is generally a slow-growing process and early detection and treatment is directed at extending life well beyond the decade following diagnosis.
The age at which to stop screening needs to be individualized, since “functional” age trumps “chronological” age and there are men 75 years old and older who are in phenomenal shape, have a greater than 10-year life expectancy and should be offered screening. This population of older men may certainly benefit from the early diagnosis of aggressive prostate cancer that has the potential to destroy quantity and quality of life. However, if a man is elderly and has medical issues and a life expectancy of less than 10 years, there is little sense in screening. Another important factor is individual preference since the decision to screen should be a collaborative decision between a patient and their physician.
PSA screening detects prostate cancer in its earliest and most curable stages, before it has a chance to spread and potentially become incurable. PSA screening has unequivocally reduced metastases and prostate cancer death and it is recommended that it be obtained annually starting at age 40 in men who have a greater than a 10-year life expectancy. PSA testing in men who have been diagnosed with prostate cancer provides valuable information about pretreatment staging, risk assessment and monitoring after treatment. Although PSA has many shortcomings, when used intelligently and appropriately, it will continue to save lives.