Many men who choose to get a prostate specific antigen (PSA) test may not need to repeat the test as frequently as previously thought, according to data from the Prostate, Lung, Colorectal and Ovarian (PLCO) trial, sponsored by the National Cancer Institute (NCI). Results will be presented as abstract #4 in the general plenary session at the annual meeting of the American Society of Clinical Oncology (ASCO) in Orlando, Fla., on Monday, May 20, 2002.

"Men who choose PSA testing now have a scientific basis for choosing, with their physicians, how frequently they wish to be screened," said John Gohagan, Ph.D., NCI project officer for the trial.

The current analysis is based on results from almost 30,000 men enrolled in the PLCO trial who had annual PSA tests as part of the study. The researchers found that, in men with an initial PSA value between 0 to 1 ng/ml (nanogram of antigen per milliliter of fluid), 98.7 percent would continue to have PSA levels below 4 ng/ml through four additional years of PSA testing. Men whose last PSA was less than 1 ng/ml may want to consider screening less often than annually.

For men with initial PSA readings of 1 to 2 ng/ml, the investigators found that 98.8 percent would have a reading below 4 ng/ml in the subsequent year. For men with readings in the 2 to 4 ng/ml range, the chances that the PSA would rise to at least 4 ng/ml were higher. This was especially true for men in the 3 to 4 ng/ml range, because 24 percent of them would show elevated readings within a year and 83 percent would show elevated levels within four years, according to the PLCO data. Doctors often use the value of 4 ng/ml or greater as the trigger for further investigation, such as a prostate biopsy.

PSA testing is frequently used in an attempt to detect prostate cancer at an early stage. PSA is a protein produced by both normal and cancerous prostate cells and its levels can be elevated in men with prostate cancer or some non-cancerous conditions, such as benign prostatic hyperplasia or prostatitis. Many men over age 50 may have early, undiagnosed prostate cancer. Most of these cancers will remain harmless, but some will progress to clinically significant disease, according to autopsy studies done in recent years.

Since the late 1980s, PSA tests have been used by a large number of men. However, PSA testing has never been proven to reduce the risk of dying from prostate cancer. Elevated PSA readings many not always be indicative of an aggressive cancer and false positive results could lead to unnecessary invasive procedures and attendant risks; thus, PSA testing is not a universally recommended screening procedure.

"This is one of the first of many important pieces of research that will come from the PLCO study," said first author E. David Crawford, M.D., University of Colorado, Denver. "But we are not yet able to address the value of PSA testing itself, and those results will come in the future when more data from the trial have been assembled and analyzed."

The PLCO trial completed enrollment in September 2001. Screening of participants with annual PSA tests and other exams will continue until 2007, and follow-up will then continue in order to determine the benefits or harms of screening.

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