Study: No specific PSA cutoff yields high sensitivity, specificity

A new study appearing in JAMA (2005; 294:66-70) suggests there is no specific PSA value that has both high sensitivity and specificity for monitoring healthy men for prostate cancer, but rather there is a continuum of prostate cancer risk at all values of PSA.

Ian M. Thompson, MD, of the University of Texas Health Science Center at San Antonio, and colleagues conducted the study using data from the Prostate Cancer Prevention Trial to determine the effectiveness of PSA testing by estimating the receiver operating characteristic curve for PSA. The team selected 8,575 men in the trial's placebo group who had at least one PSA measurement and digital rectal exam in the same year. Of these, 65% had at least one biopsy, and of these, 21.9% were diagnosed with prostate cancer.

PSA cutoff values of 1.1 ng/mL, 2.1 ng/mL, 3.1 ng/mL, and 4.1 ng/mL yielded sensitivities of 83%, 52.6%, 32%, and 20.5%, respectively, and specificities of 38.9%, 72.5%, 86.7%, and 93.8%, respectively, according to the authors. They said a clear-cut decision rule for prostate biopsy based on PSA values would be challenging to derive from these data, and no single cutoff exists that would simultaneously yield both high sensitivity and high specificity.

"Patients and health care professionals must be re-educated that there is a continuum of risk and no clearly defined PSA cutpoint at which to recommend biopsy," the authors wrote. "It will be the patient, in concert with his health care professional, who will ultimately have to weigh the sensitivity-specificity tradeoffs in combination with the uncertain natural history of the disease to determine whether further evaluation with a prostate biopsy is appropriate."