Most men between the ages of 50 and 70 don't need to have blood tests for prostate cancer every year, according to researchers at the Johns Hopkins University School of Medicine.
Prostate cancers grow so slowly, the study said, that a test every two years for the substances the body produces in response to the cancer will give doctors enough time for effective treatment.
The longer intervals will also avoid the costs of unnecessary testing.
Even if a cancer turns up during the two years between tests, " it's not growing to a point where it's not curable," said Dr. Jonathan I. Epstein, a Hopkins professor of pathology, urology and oncology, and a co-author of the study.
In a separate study, another team of scientists at Hopkins and two other institutions reports improvements to a set of statistical tables that helps doctors and their patients use related test results to find treatments most likely to give them a favorable outcome.
An earlier version of the tables, which resemble railroad timetables, has already led to a 20 percent improvement in the percentage of men whose prostate surgery turned out to have been the right choice for them.
The studies were reported in today's issue of the Journal of the American Medical Association.
Prostate cancer is the most commonly diagnosed cancer among men in the United States. More than 317,000 new cases were found in 1996, and more than 41,000 men died.
There is considerable debate over whether a test for prostate specific antigen (PSA) is needed every year, Epstein said. Urologists generally recommend it, but primary care physicians will often opt for PSA tests every other year.
The tests typically cost only $25 each, but last year more than 25 million were performed in the United States. "It's a huge number," Epstein said.
Because they are often regarded as screening tests, however, some insurance plans won't pay for them, and the costs are borne directly by patients.
The study used data from the Baltimore Longitudinal Study of Aging. It compared the annual blood tests of prostate cancer patients with those of men with no evidence of the disease.
Led by urologist Dr. H. Ballentine Carter, the Hopkins team found that if a patient's PSA level is less than 2 (nanograms per milliliter) in his first test, he isn't likely to develop an incurable cancer before a second test two years later.
"For these men, it's safe to wait an extra year," said Carter. "And because 70 percent of men age 50 to 70 have PSA levels less than 2, we can eliminate a lot of unnecessary testing."
In men with PSA levels between 2 and 4, 94 percent of any cancers found after two years will be limited to the prostate gland and curable with surgery. With PSA values between 4 and 5, Epstein said, 89 percent of cancers will be curable, but PSA tests should be more frequent.
A PSA of 5 or more calls for a biopsy and possible treatment with surgery or radiation, Epstein said.
In the second study, researchers unveiled an improved version of a set of charts, or "nomograms," that doctors can use to convert the results of a patient's rectal exam, tissue studies and PSA tests into a treatment decision.
The big issue in prostate cancer, Partin said, is whether the cancer has spread beyond the prostate gland.
If the cancer remains confined to the prostate, surgery may cure it. Many patients, to survive, will choose to risk the urinary incontinence and sexual impotence that can result from surgery.
If the cancer has spread, however, a cure is unlikely. If patients could know in advance that their cancer has probably spread, many would reject surgery in order to avoid the incontinence and impotence that would mar the quality of their remaining time.
The nomograms can give them the statistical information they need to determine how often men with the same test results turned out, after surgery, to have spreading cancers that surgery couldn't cure.
"These tables don't tell you whether you're going to be cured or not, just -- of 4,000 men with the same test results as you -- how they fared," Partin said.
An earlier version of the nomograms was based on the experience of 800 patients. After it was introduced in 1993, the percentage of operable cancers found in surgery jumped from 33 percent to 55 percent.
The latest version is better because it is based on a much larger sample of cancer patients, and it is supported by a broader base of statistical analysis, Partin said.
But the basic guidance it offers has not changed.
Pub Date: 5/14/97