The value of the PCA3 test: a multi-center study

The prostate cancer antigen 3 or PCA3 test was initially approved as an aid to the assessment of risk of prostate cancer in men with an elevated PSA level who had already been given at least one prior, negative biopsy. This test has also been used by some physicians to assess risk of prostate cancer in men who have never had an initial biopsy and to assess risk for clinically significant as opposed to indolent prostate cancer (see here for more information).

The cut-point for elevated risk suggested by the PCA3 test was initially stated to be a PCA3 score of about 35. However, there have long been significant questions about the accuracy of that cut-point. As a consequence, the National Cancer Institute conducted a prospective validation trial to assess the diagnostic performance of the PCA3 test for the detection of prostate cancer among men previously screened with PSA (i.e., men with an elevated PSA level of 2.5 to 10 ng/ml or some other significant risk factor who had not had a prior biopsy).

Wei et al. have now reported the results of that study, which enrolled 859 men at 11 different centers here in the USA between December 2009 and June 2011. Here are the key results of that study:

  • The average (mean) age of the patients was 62 years.
  • All enrolled patients had previously been scheduled for a biopsy and were given a PCA3 test.
  • Patients who had a negative result on a first biopsy but were still to be considered at risk for prostate cancer were given a repeat biopsy.
  • The positive predictive value (PPV) of a PCA3 score of > 60 was 80 percent in the initial biopsy group (i.e., among men who went on to have a first biopsy).
  • The negative predictive value (NPV) of a PCA3 score of < 20 was 88 percent on a repeat biopsy (i.e., among men who had already had at least one prior negative biopsy)
  • The addition of the PCA3 test to individual risk estimation models (which included age, race/ethnicity, prior biopsy, PSA, and digital rectal examination) improved the stratification of cancer and of high-grade cancer.

Wei et al. conclude that their data

independently support the role of PCA3 in reducing the burden of prostate biopsies among men undergoing a repeat prostate biopsy. For biopsy-naive patients, a high PCA3 score (> 60) significantly increases the probability that an initial prostate biopsy will identify cancer.

Having said that, however, this information still needs to be treated with great care for two reasons:

  • There have been many reports of men with PCA3 scores of > 100 who have been found to be negative for prostate cancer after multiple biopsies (and there remains a 20 percent chance that a man with a PCA3 score of > 60 will have a negative initial biopsy result based on the current study)
  • Based on the data from this study by Wei et al., the clinical value of any PCA3 score between 20 and 60 appears to be of relatively limited value.

As a consequence, the real clinical value of the PCA3 test in any one individual patient remains somewhat unpredictable. It will be interesting to see what effect these data have on guidelines issued  by such organizations as the National Comprehensive Cancer Network and the American Urological Association regarding testing of men for risk of prostate cancer and determination of whether biopsies should be carried out — especially among men with a PCA3 score of 20 to 60.

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