Screening for prostate cancer has operated in Germany since 1978 and rectal examination is included in insurance annual check-ups in Belgium. In France, work-site PSA screening has been launched by Occupational Health Services for men aged 50-65. However, no consensus exists on the validity of such screening. The US National Cancer Institute stated there is insufficient evidence to establish that a decrease in mortality from prostate cancer occurs with screening by DRE, TRUS, or serum markers; yet the American Urological Association and the American Cancer Society have published guidelines advocating annual DRE and PSA testing for men over the age of
50. Although formal screening is not taking place widely, there is certainly marked case finding in many parts of the world.
There have been a number of small screening studies, but many rely on volunteers willing to respond to invitations for screening and this introduces selection bias.
The cancers that are confined to the prostate can be slow-growing and may be biologically insignificant as far as the patient is concerned, and yet 70% of tumours detected through screening are organ-confined and could potentially be eradicated by radical prostatectomy. This eradication is measured by undetectable PSA levels for up to 10 years after surgery.
Slowly growing or latent tumours may be more likely to be detected by screening but might have a longer pre-clinical course. The rate of detection of these tumours would increase if the screening was applied over a number of years.
Other factors that must be addressed before the introduction of screening include the morbidity of screening—the unnecessary anxiety it induces, especially for a high proportion of men found to have a falsely positive initial result. Finally, and probably most importantly, there is lack of true evidence regarding the effective treatment for early prostate cancer.
There is a debate as to the desirability of including DRE at the initial screen. Although its use will increase the number of cancers detected, there is some evidence that DRE may miss life-threatening tumours. Although in two GP studies in the UK, DRE and PSA were acceptable to members of the general male population, in larger pilot studies in Belgium and the Netherlands acceptance rates were as low as 35-40% when both tests were used. Acceptance rates in UK males of screening for other diseases by blood tests are of a higher order, up to 60%.
The combination of serum PSA and DRE screening results in a higher overall cancer detection rate than each used in isolation— 4-6%. This means, however, that 20% of the screened population will require biopsy. If PSA is used alone, three patients must undergo biopsy to find one case of prostate cancer. In PSA-based screening, over 97% of cancers detected on initial evaluation are clinically localized to the prostate.
The case for screening would therefore appear to be strong, except for one major flaw: there have been no randomized controlled trials with sufficient power to detect any improvements in mortality from medical intervention. Two trials evaluating randomized treatment of prostate cancer after detection—the PIVOT study in the US and a smaller Scandanavian study—will soon report.
In those patients who have organ-confined prostate cancer, about 90% are free of PSA relapse at five years after radical prostatectomy, as are about 70% of men with only focal capsular penetration. Prior to
PSA testing, many patients were found to have positive lymph nodes, but the trend now is to operate on patients with lower PSAs and to focus on those who can theoretically be cured.
The absence of data to support prostatic screening does not mean such a benefit may not exist.
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