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Do Prostate Cancer Tests Improve Prostate Cancer Prognosis?


by John R. Lee, M.D.

Question from a Reader:

Dr. Lee, I understand that prostate cancer detection techniques include digital rectal exam, a blood serum test called prostate specific antigen, and something called transrectal ultrasonography. Can you tell me how accurate these tests are?

Answer:

Digital rectal exam (DRE), manually feeling the prostate via the rectum, is the historic primary test of the prostate. Only the posterior aspect of the prostate can be felt. The examiner is interested in general size of the prostate, its consistency, and any lumps or irregularities in shape.

Prostate specific antigen (PSA) is a substance present normally in prostate tissue. Elevated levels correlate loosely with increased probability of cancer. Newer tests measure various analogs of the antigen, some of which are thought to be more specific for cancer, per se. Further research is needed to validate their significance.

Transrectal ultrasonography (TRUS), uses a rectal probe for detecting sound wave reflections (like submarine sonar) to create a picture of the prostate. It can show small irregularities within the tissue of the prostate. It is considered the gold standard for early detection of prostate cancer. If irregularities are found, needle biopsy follows to determine the nature of the irregular areas.

According to a recent evaluation published in the Journal of the National Cancer Institute, a group of 10,523 men aged 54-76 years were screened by all three tests with the following results.

When all three tests were used, 473 (4.5%) of the men were found to have prostate cancer. DRE alone detected 264 men with prostate cancer, or 55.8% of the total as found by TRUS. However, in those men with prostate cancer and having PSA levels less than 3 ng/ml (the supposed normal or safe range), DRE detected only 4-11% of the cancers. In those men with PSA levels of 3-9 mg/ml, the DRE detection rate was 33-83% depending on skill of the examiner and the level of PSA. The higher the PSA level, the greater was the detection rate by DRE.

PSA level was also found to be not an especially good indicator of prostate cancer. If only PSA levels were used, 82 (17.3%) of the 473 cancers found by TRUS would have remained undetected. Moreover, among men with cancer and a PSA level of less than 4 ng/ml (usually considered a safe level), 42% of the cancers were termed minimal, 42% termed moderate, and 16% were advanced.

An important question remains. The clinical significance or ultimate difference in outcome of prostate abnormalities found by TRUS in men of this age with normal PSA levels is, as yet, unknown. If found and treated by todays methods, is the mortality rate truly altered? It is possible, even likely, that small islets of cancer develop slowly in the prostate and never go on to become metastatic, life threatening, or have any effect whatsoever on a persons health. Our tests can not yet distinguish these differences.

The age at which these tests should be used is also open to question. Prostate cancer does occur in men younger than 54. The incidence of this is presumably small, but is it sufficient to recommend annual testing? Is so, which test or tests would be appropriate? Is the cancer more aggressive in younger men? If more aggressive, do our treatments work?

Source: Schroder FH, et al. Evaluation of the digital rectal examination as a screening test for prostate cancer. J National Cancer Institute 1998; 90(23): 1817-1823.