In ongoing PSA debate, scales tip in test's favor.
The debate centers on the reliability of the test, which even proponents admit is less than stellar. It has high rates of false positives and negatives, causes large numbers of unnecessary biopsies, and, in rare cases, can lead to unnecessary prostectomies. It is even unclear whether early detection actually benefits patients.
A study published in the March 2000 issue of Epidemiology found that prostate cancer mortality rates have dropped since the introduction of the PSA test in 1986 (The Wall Street Journal. April 25, 2000:B1-B4). The study, conducted by researchers at the National Cancer Institute in Bethesda, MD, found that among men between ages 60 and 79, death rates are lower than they were in 1950. Among Caucasians, mortality rates dropped 16% in the past 10 years. Among African-Americans, who are at greater risk for the disease, death rates dropped about 11%, the study found.
A paper displayed at the American Urological Association in Atlanta, GA, this April found even stronger data (The Wall Street Journal. April 25, 2000:B1-B4). European researchers tracked prostate cancer deaths in Tyrol, Austria, where 65,000 men ages 45 and 75 were given free PSA screenings starting in 1993. When compared to the death rates in unscreened provinces of Austria, mortality rates in Tyrol were down 32% in 1997 and 42% in 1998, researchers found.
Additionally, recent findings have suggested that the efficacy of the PSA can be improved. A study presented at the American Association for Cancer Research on April 2 suggests that measuring levels of free PSA might reduce the number of unnecessary biopsies brought on by the test (Reuters Medical News). Men with cancer have lower levels of free PSA than men whose higher PSA readings are caused by other factors, such as benign prostatic hyperplasia or prostatitis. By measuring the amount of free PSA in those with borderline PSA levels, doctors can more accurately spot patients with cancer.
Many clinicians are using free PSA counts today, according to Peter H. Gann, MD, who worked on the study; but there are no established standards as to what levels of free PSA constitute a higher risk for prostate cancer. Generally, if normal PSA is more than 10 ng/mL, the patient has even odds of having cancer. The gray area lies between 4 and 10 ng/mL. Dr. Gann recommends that clinicians establish the cutoff at somewhere between 20-40% of free PSA and possibly lower the normal PSA cutoff to 3 ng/mL to increase PSA testing accuracy and keep the undiagnosed rate at well below 10%. He hopes future studies will fix a more precise standard.
Other modalities can be used to double-check PSA tests. At the American Association for Cancer Research, a study predicted that signs of hypermethylation at the glutathione-S-transferase gene in urine could serve as a red flag for prostate cancer, according to Reuters Medical News. And a recent report in Cancer concluded that patients diagnosed with prostate cancer and having a Gleason sum of 6 or less, PSA levels of 10.6 ng/mL or lower, and clinical TNM stages of T2a or below are at lower risk for lymph node metastases (Reuters).
The recent studies have caused some physicians to 'rethink the test. "I was originally very much a skeptic," University of Texas urologist Ian Thompson, MD, told the New York Times (May 2, 2000:F1-F5)., But now he credits screenings with decreased mortality rates. Otis Brawley, MD, a National Cancer Institute researcher and for years a skeptic, told The Wall Street Journal he believes the test is partly responsible for lowering death rates (April 25, 2000:B1-B4).
"There is no value like the PSA test," says Richard N. Atkins, MD, vice chairman of the National Prostate Cancer Coalition, a supporter of routine PSA screens. "Many men believe it has saved their lives. What we [the coalition] are asking is this: Please let's resolve this controversy now before public health policy becomes a matter for legislation."
Yet the controversy is far from being resolved. Critics note that recent plunges in death rates might have more to do with newer, aggressive treatment methods than with PSA screens. Perhaps most significantly, PSA screening has never cleared the hurdle of a double-blind, randomized, placebo-controlled clinical trial.
The American College of Physicians and the American Academy of Family Physicians urge their members not to push for routine PSA screening but instead suggest that patients be counseled about the faults of the test and allowed to make their own decisions.
PSA screening may indeed facilitate early detection of prostate cancer, allows Richard Roberts, MD, JD, a professor of family medicine at the University of Wisconsin. However, "[t]here is not a single study that indicates early detection improves quality of life or mortality rates. The position I take with patients is that I tell them, 'I don't know ... whether the test is beneficial.' I think there is a small percentage of patients who will benefit from early detection, but I don't know who those patients are."
Dr. Roberts notes that prostate cancer is a serious health problem but one medical science can do little about. Studies have shown that 100% of men over age 90 have some form of the disease, yet only 3% ever die from it. In many cases caught by PSA tests, therapy is unnecessary.
While the benefits of the PSA are theoretical, the risks are well known, he says. One-third of positive PSA results are caused by conditions other than prostate cancer; one-fourth of the results are false negatives. Once found, treatment of the disease can be devastating: 75% of prostectomies lead to impotence; 25% of prostectomy patients will be left incontinent; and 10% will wear diapers for the rest of their lives.
If a patient has a family history of the disease, Dr. Roberts says he will explain the PSA test and the risks involved. Sometimes the patient will opt for the test, but often not; many patients do not wish to risk the quality of their lives for the theoretical benefit of living longer, notes the doctor.
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|Title Annotation:||prostate specific antigen (PSA) blood test|
|Publication:||Medical Laboratory Observer|
|Article Type:||Brief Article|
|Date:||Jun 1, 2000|
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