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Ontario Prostate Specific Antigen (PSA)
I. PSA TESTING : Screening
Some Commonly Asked Questions
We still do not know what causes prostate cancer. Factors associated with higher rates are increasing age (especially over 50), family history of the disease (one or two first-degree relatives, such as a father or brother), and black race. We are not yet sure how much other factors, such as a diet low in fibre or high in fat, or low levels of physical activity, play a role.
The symptoms of early-stage prostate cancer are similar to other common prostate problems associated with aging, such as benign prostatic hyperplasia (BPH). They include the following: urinating more frequently, especially at night; having difficulty in starting the urine stream, or feeling a need to push or strain to start urinating; having a weak or interrupted urine stream; or feeling that the bladder is not completely empty. Urinary symptoms are particularly likely if the cancer is located near the bladder or the urethra. Pain or discomfort is not a typical early presenting symptom in prostate cancer; however, it is a common symptom of bone metastases, when the disease is no longer curable.
Of every 100 asymptomatic men, about 10 will be diagnosed with prostate cancer during their lifetime, and 3 of the 100 will die from the disease. These numbers may increase as therapies for other illnesses in the elderly improve. It is important to understand that some men with prostate cancer who do not die of the disease will nonetheless have disease progression whether or not they are treated initially, and may have a lower quality of life as a result.
It is important to distinguish clinically significant prostate cancer from cancer that is slow-growing and non-life-threatening. "Clinically significant" means that leaving the cancer untreated would result in symptoms requiring treatment or would lead to mortality.
Prostate-specific antigen (PSA) is a protein produced by prostate tissue. An elevated PSA level in the blood may identify the presence of cancerous abnormalities of the prostate gland before symptoms are reported, and thus has been used as a screening test. The limitation of PSA as a diagnostic test is that PSA levels can be elevated in benign diseases of the prostate as well as in malignancies.
A PSA value of >4.0 ug/L has often been defined in the literature as abnormal and is frequently used as a cut-point. However, a man's PSA level increases steadily as he ages, and some-not all-urologists advocate the use of age-related "normal" PSA cut-points, rather than using >4 ug/L for all. The table below shows suggested age-specific ranges.
Source : Oesterling JE et al. JAMA 1993; 270:860
If a PSA test is close to the cut-off value, you may decide to repeat it to make sure it is not a laboratory error. You might immediately investigate your patient for prostatic enlargement, infection or cancer if the PSA is above the cut-off value.
What is the accuracy of the PSA test?
For every 100 men over the age of 50 who have the PSA test :
Most abnormal PSA results are caused by BPH. Very high PSA levels usually occur in men with advanced or metastatic prostate cancer, but such high levels are rarely seen in men with early disease.
What factors might have a misleading impact on the test result?
Any of the following can cause PSA levels to fluctuate modestly: prostate manipulation during digital rectal examination, transrectal ultrasound (TRUS), biopsy, presence of infection, strenuous exercise, ejaculation and normal day-to-day variation, to mention a few. See Table IVa in Section IV for a more comprehensive list.
The way that the blood is drawn and stored for testing may also affect the PSA level. See Table IVb in Section IV showing important factors in blood collection characteristics.
Are there other screening tests for prostate cancer?
Another test used is the digital rectal examination (DRE), which is considered part of routine medical care. However, certain factors limit its sensitivity for prostate screening. The examiner can palpate only the posterior and lateral aspects of the prostate - and up to 40% of tumours occur anterior to the prostate midline, so they can't be felt. Moreover, stage A (early) tumours are not palpable by definition. Various studies have reported a wide range for the sensitivity of DRE, from a low of 18%-22% up to 55%-68%; limited specificity is also reported, producing a considerable number of false-positive results. These facts provided the platform for the Canadian Task Force on the Periodic Health Examination "Category D" recommendation for DRE. The recommendation may be revisited when considered in combination with PSA testing. Finally, there is as yet no evidence that screening with isolated DRE in asymptomatic men reduces prostate cancer mortality.
Transrectal ultrasound (TRUS) has also been proposed as a screening test. This technology documents prostate volume and detects areas of the prostate that are suspicious for cancer, as cancerous tissue is frequently hypoechoic. However, it is not an alternative to DRE, and a normal TRUS does not eliminate the possibility of cancer. It is most useful for further prostate evaluation, and provides guidance for the urologist or radiologist when performing a prostatic biopsy. The combination of PSA and DRE is as sensitive as TRUS for establishing a suspicion of cancer.
What do I need to consider in determining if PSA screening is appropriate for a patient?
The whole issue of the benefit of screening must involve consideration of the success of treatment of early-stage prostate cancer. There are three generally accepted treatments for prostate cancer, however detected: "watchful waiting" (also called "delayed therapy" or "expectant management"), prostatectomy (surgery) and radiation therapy.
All three treatments have their associated risks, and all have significant potential effect on quality of life (QOL) issues. Data on treatments and outcomes are reviewed in Appendix A.
Are there specific circumstances where screening PSA tests are definitely not recommended?
Since PSA testing for screening purposes in asymptomatic men is of uncertain benefit, performing it on men whose life expectancy is less than ten years is potentially inappropriate, as it is likely that most of their morbidity and mortality will be related to disease processes other than prostate cancer. However, there is no consensus on an upper age limit. In asymptomatic men, PSA testing for screening purposes is of uncertain benefit.
Should I advise my patients to be screened with the PSA test-or not? What do the experts say?
There are no general statements about screening that are applicable to all men. Even the experts disagree. Canadian and American organisations that have a policy on using the PSA test to screen asymptomatic men do not recommend population-wide screening rather they endorse the importance of informed choice.
As mentioned earlier, much of the disagreement over routine screening involves quality of life issues. It seems that the most difficult part of the screening question boils down to two issues: one philosophical, one definitional. Philosophically, some physicians (and members of the public) believe that despite the lack of accuracy of the PSA test and the attendant morbidity of potentially unnecessary treatment, all men over the age of 50, and those at high risk (first-degree relatives with prostate cancer and/or black race) over the age of 40, should be tested for prostate cancer.
But then there is the definitional issue. At about age 50, most men start having at least some symptoms of prostatism: it's a normal part of the aging process for males. Most men who attend their family physicians regularly will have a DRE as part of a check-up. When there are no findings on the DRE and the patient has no symptoms, doing a PSA test is not recommended. But if the examining physician feels a change in the prostate-thickening, asymmetry, nodule, and/or focal lesions-then combining DRE with a PSA test moves from being a screening test to being an investigative manoeuvre. PSA testing as a stand-alone, isolated screening test in asymptomatic males is not the same as coupling it with suspicious DRE findings to investigate or rule out disease, be it BPH or prostate cancer. Simply put, screening is not the same as investigation and diagnosis (see Section II)-a distinction that needs to be underscored.
All the information you have just read is pertinent when helping your individual male patients with their screening decisions. It is essential for all men to be fully informed and aware of the potential consequences of their decision to be screened or not screened. The evidence to support PSA testing as a screening tool is limited. The spectre of lifelong urinary incontinence and/or erectile dysfunction following prostatic surgery and/or radiation makes the decision very difficult for many men, particularly when they take into consideration that some prostate cancers are slow-growing or never become life-threatening.
What do I tell my patients if they say, "Isn't finding cancer early supposed to improve my chances of cure?"
Generally, this is true with respect to people who have symptoms of cancer, but it is not always the case when tests are applied to people who do not have symptoms. We know that the screening of asymptomatic women for cervical cancer by PAP smears and the screening of asymptomatic women aged 50 and over for breast cancer by mammography save lives. However, screening younger women for breast cancer and screening for lung cancer have not been shown to reduce cancer mortality. These experiences have taught us that not all screening tests necessarily result in decreased deaths from a particular cancer.
There is some reason to hope that PSA screening for prostate cancer may save lives. DRE, coupled with PSA measurement, may increase early detection and may improve quantity and quality of life. However, until we know definitively, men should be made aware of the potential risks and benefits of early detection so that they can make an informed decision about being screened. They need to understand that screening is a process, and that this process may continue through to having to make decisions about treatment and experiencing side effects as a result of that treatment.
Is PSA testing for screening purposes insured?
No. Although the Ontario Ministry of Health endorses the PSA Clinical Guideline Expert Committee's recommendation that men be well-informed and understand the ramifications of PSA testing, and supports development and dissemination of educational materials for both physicians and their patients, PSA testing for screening purposes in asymptomatic males is not insured in Ontario. Asymptomatic men who, with the help of their family physician, make an informed decision to be tested and who feel it is important to their well-being must understand that they will have to pay for the test themselves.
What's the bottom line on using the PSA test for screening for prostate cancer in asymptomatic males?
According to the Ontario Prostate Specific Antigen (PSA) Clinical Guidelines,PSA determination should not be used as a population-wide mass screening test for the early detection of prostate cancer in asymptomatic males
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