Some Men with Low PSAs Have Prostate Cancer: Most Cancers Found Are Not Likely to Be Clinically Significant
Men with low PSA (prostate specific antigen) levels on screening tests can still have prostate cancer, according to a study released today by scientists from the National Cancer Institute (NCI), part of the National Institutes of Health, and the Southwest Oncology Group, an NCI-funded network of researchers. In this study, prostate cancers were detected by biopsy in men with normal PSA levels.
"The good news is that the vast majority of these cancers were low and intermediate grade, which often are not clinically significant," said Leslie Ford, M.D., associate director for clinical research in NCI's Division of Cancer Prevention, who participated in the research.
"This was the first systematic study of men with PSA levels from 0 to 4 nanograms per milliliter (ng/ml). It shows that cancer of the prostate can be present in men with 'normal' PSAs," said Ian Thompson, M.D., University of Texas Health Science Center at San Antonio, who led the study. Doctors often use the value of 4.0 ng/ml or greater as the trigger for further investigation, such as a prostate biopsy. A PSA level below 4.0 is generally considered normal.
Prostate cancer clinicians often say that men are much more likely to die with prostate cancer than from it. According to recent autopsy studies, many men over age 50 have early, undiagnosed prostate cancer. Clinicians concur that most early cancers remain harmless, though some may progress to clinically significant disease.
The 2,950 men in this study were from the "control arm" of the Prostate Cancer Prevention Trial (PCPT), an NCI-funded study that found in 2003 that the drug finasteride reduced by 25 percent a man's chances of getting prostate cancer.
Men in the control arm were given a placebo, or sugar pill, instead of finasteride and, like the men on the finasteride arm, received annual prostate screening for seven years with a PSA test and a digital rectal exam (DRE). All men in PCPT entered the trial at age 55 or above, had an initial PSA level of 3 ng/ml or less, and a normal DRE. All were asked to undergo an end-of-study prostate biopsy. The report released today focused on men at low risk of having prostate cancer