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PSA screening

By: Dr. Rich Bevan-Thomas, M.D.
Medical Director of USMD Prostate Cancer Center

The prostate-specific antigen (PSA) blood test is a useful marker to detect prostate cancer. In fact, a majority of men diagnosed with prostate cancer over the last 2 decades underwent a prostate biopsy because of an abnormally elevated PSA. Despite its obvious utility in diagnosing patients with early localized prostate cancer, many men have undergone repeat biopsies because of an elevated PSA with no evidence of prostate cancer. In addition, controversy surrounds the precise cutoff point in which men should undergo a biopsy. Traditionally, urologists recommended a prostate biopsy for men with a PSA greater than 4.0; however over the last several years this cutoff level has been challenged. There are now a number of factors involved in the decision tree for recommending a prostate biopsy for men. These include the age of the patient, the PSA velocity and the percent free PSA.

PSA is a protein that is responsible for liquefying fluid in the ejaculate and is a normal product of the prostate gland. All men with a prostate therefore will have some detectable level of PSA on a blood test. Patients with prostate cancer, however, usually have an elevated PSA level. PSA can be divided into a complex and percent free PSA. Prostate cancer has been associated with a lower percent free PSA and men with a low percent free PSA (less than 12%) have an increased chance of harboring a focus of cancer. The PSA can be elevated for other reasons besides prostate cancer including infection, inflammation, urinary retention and benign enlargement of the prostate. The only way to diagnose prostate cancer is to perform a prostate biopsy (routinely performed in the office setting under ultrasound guidance).

PSA as a screening tool for prostate cancer was first described in 1991 by Dr. Catalona who concluded that the PSA was more accurate than the traditional digital rectal exam. Currently, both the digital rectal exam and PSA are used together to evaluate men at risk for harboring a focus of prostate cancer. Although the PSA test is very helpful in diagnosing patients with prostate cancer at an early stage, the exact number which should trigger the need for a biopsy continues to be debated. The American Urologic Association recommends a prostate biopsy for patients with a total PSA greater than 4.0, a suspicious digital rectal exam or significant change in the PSA velocity (PSA increase of 0.75 ng/ml over 12 months).

A recent paper published by Dr. Moul and colleagues atDuke University addressed several of the issues regarding the PSA threshold and PSA velocity in the Journal of Urology in February 2007. In this study, 11,861 men were evaluated over a 2 year period. The investigators found that using a PSA cutoff value of 2.0 and a PSA velocity of 0.4 ng/ml per year for men aged 50 to 59 had a higher sensitivity of detecting prostate cancer than using the standard cutoff of 4.0 and the standard PSA velocity of 0.75 ng/ml per year. The team therefore concluded that PSA velocity and PSA cutoff levels could be decreased in younger men.The bottom line on the PSA controversy is that there are multiple factors involved in recommending a prostate biopsy for men. Younger men with a mildly elevated PSA may require an earlier biopsy and more aggressive surveillance than older men. In addition, PSA velocity continues to play an important role as well to detect patients with early localized prostate cancer to improve the chances for cure.

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