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Prostate cancer - the American male's silent killer.

Prostate cancer, the most common of all cancers, affects three out of 10 American men age 50 or older--and that figure climbs to seven out of 10 for men over 70! Fortunately, most of these prostatic cancers are so small and grown so slowly that they cause neither illness nor death. Nonetheless, cancer of the prostate is second only to lung cancer in causing death from cancer in American men.

Unfortunately, there is no way to predict whether an individual with prostate cancer in its earliest form will go on to develop a serious form of the disease. It is therefore desirable to detect the presence of cancer of the prostate as early as possible so that it may be removed before it has opportunity to do so.

Until fairly recently, the only screening test for prostate cancer was the digital rectal examination (DRE)--feeling the prostate with a finger inserted into the rectum. DRE is a simple procedure, and although some patients object to it because of discomfort or embarrassment, no routine physical examination of an adult male is complete without it. Nevertheless, despite the high incidence of prostatic cancer, the DRE is able to detect the presence of the cancer in relatively few cases--as few as 1 to 2 percent, by some estimates.

A relatively new procedure, transrectal ultrasonic examination of the prostate (ultrasonography), has shown much better results. A thin fiber optic probe is inserted into the rectum to produce an ultrasound image of any changes in the prostate tissue's density that might suggest the presence of cancer. Most physicians, however, consider the procedure to be too expensive to justify its use in routine physical examinations.

Several years ago, a blood test was developed to detect the presence of a substance called prostate-specific antigen (PSA)--a substance produced exclusively by cells of the prostate gland. PSA is, however, produced by normal prostatic cells, as well as abnormal ones, so that its presence at abnormal levels does not necessarily indicate the presence of cancer. Elevation of PSA in the blood can occur with the prostatic enlargement that affects nearly every man in later years, or with inflammation of the prostate.

PSA is also thought to rise immediately following digital examination of the prostate, and blood should thus be drawn for the PSA test before the digital examination is performed. Measurement of PSA has been used to monitor the progression of known prostate cancer and the response to therapy, but until recently it has not been widely used as a screening test.

In April 1991, a team of researchers at the Washington University School of Medicine in St. Louis reported on the use of PSA as a screening test for prostate cancer. PSA was measured in 1,653 healthy males 50 years old or older. Men with serum PSA levels below 4 micrograms per liter were measured again six months later. Those showing a level of PSA above 4.0 at the first or subsequent examination then underwent both digital and ultrasonic rectal examinations. If either or both of these procedures showed suspicious findings, doctors performed a biopsy on the prostate.

Among the men studied, 92 percent had initial PSA levels below 4.0; 6 percent were in the 4.0-9.9 range; and 2 percent were 10.0 or above. Among the 102 men in the 4.0-9.9 range, 85 had biopsies; 19 proved to have cancer. Among the 30 men in the 10.0 or above range, 27 had biopsies; 18 had cancer. Thus, of the total of 112 men who had biopsies, 37 had cancer.

Those statistics are important for a number of reasons. Among the 37 men found to have cancer, rectal examination alone would have missed the disease in 12 of them (32 percent). On the other hand, if we assume that 30 percent of men over 50 have prostatic cancer, we see that the disease was missed in a very large percentage of the 92 percent who had normal PSA values.

The authors of the study concluded that "serum PSA measurement is a useful addition to rectal examination and ultrasonography in the detection of prostate cancer and that it is the most accurate of the three tests for this purpose. Our results suggest that measurement of PSA and rectal examination combined, with the addition of ultrasonography in patients with abnormal findings, will provide a better method of detecting prostate cancer than rectal examination alone."

Regrettably, there is still no surefire test for prostate cancer. A normal PSA does not mean that cancer is not present. It does, however, provide a baseline to compare later measurements. At about $35, the procedure is relatively inexpensive. For men with a family history of prostatic cancer, an annual PSA test and rectal examination seem to make sense. Many doctors believe that they make sense for every man over 50, regardless of his family history.
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Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Publication:Medical Update
Date:Dec 1, 1991
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