Is PSA Passé?

Summarized by Robert W. Griffith, MD
June 30, 2005

Introduction

Recent analyses of PSA testing in connection with possible prostate cancer have led some authorities to suggest "the emperor has no clothes". In other words, the diagnostic powers of the test have been called into question - too many false positive results (a positive test in someone without cancer), and too many false negatives (a negative test in someone with cancer).

Professor E David Crawford of the University of Colorado has reviewed the situation in the medical journal Lancet; here are the main points he makes.

Screening for prostate cancer

Widespread screening for prostate cancer started in the USA in the late 1980s. At that time, the PSA test (PSA stands for prostate specific antigen) was considered the most important cancer tumor marker available. It's generally accepted that most cases of incurable disease are detected by screening, and that the death rate from prostatic cancer has decreased by 26% in the last 6 years. But whether screening is actually responsible for the decrease in the death rate is still disputed - maybe some other factor is responsible, such as increased awareness leading to earlier diagnosis, or the introduction of better treatment protocols.

Two large clinical trials are now underway to determine what is the most important factor responsible for the improved outlook for prostate cancer, but they won't be reported out for another 6 or 7 years.

The link between PSA and prostatic cancer

What's known about the relationship between PSA and prostate cancer? Clearly there's a link between the two; both PSA levels and Gleason's score¹ are good guides to the likely outcome after treatment. So for established cancer, there's definitely a role for using PSA tests.

Because of this accepted link, doctors have used the PSA as an aid in deciding whether to biopsy a suspicious prostate. A value of 4 ng/mL or more was considered a reason for doing a biopsy. More recently it's been suggested that 2 ng/mL should be the cut-off point. This means more men will undergo biopsies and the tumors detected will be more localized, so that the decisions regarding further treatment will be more difficult.

One of the reasons for the doubts surrounding PSA testing is the fact that the results are very different in 'virgin' unscreened men and in those who undergo repeated testing at intervals. In the original group of patients (in the 1980s) when tumors were in a more advanced stage (and therefore could be felt rectally in 92% of cases), PSA levels averaged 24 ng/mL. In a recent group of patients tumors could only be felt rectally in 17% of cases, and the PSA levels averaged 7.3 ng/mL.

Recent studies have shown that the rate of increase in a PSA level is important for detecting a more aggressive cancer (see the first link below).

It must be remembered that raised PSA levels are also seen with benign prostatic hypertrophy (BPH), or 'prostatism', when there is no cancer; a PSA of greater than 1.6 ng/mL is an indication of progression of BPH.

So what should the doctor advise?

As Professor Crawford points out, screening detects cancers earlier and in a curable state, but at the expense of more biopsies, the risk of treatment-related side-effects, and the over-treatment of some men. Finding a cancer, even in older men, may be helpful, because treatment can improve survival. To date, we don't have another tool that's better than the PSA for early diagnosis.

And if cancer is diagnosed, repeat PSA should be done to assess the aggression of the tumor, and the likely outcome of treatment.

Source

• PSA testing: what is the use? ED. Crawford, Editorial. Lancet, 2005, vol. 365, pp. 1447--1449

Footnotes
1. The Gleason score is made by a pathologist who looks at the biopsied prostate tissue under a microscope. He or she examines the way that the cancerous cells look compared to normal prostate cells. Although scores on the higher end of the Gleason scale (7 through 10) usually indicate a more serious prognosis, your age, emotional well-being, family support system, and physical health status are all individual factors that can influence the outcome of your disease.

Related Links
PSA - It's the Rate of Increase That Counts
A Raised PSA Result? Don't Panic!
How to Avoid Prostate Cancer?

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