The prostate cancer antigen 3 or PCA3 test is already widely used to further assess risk for prostate cancer in a man with a high PSA result (potentially indicative of risk for prostate cancer) but an initial negative biopsy. The “cut point” for re-biopsy is considered to be a PCA3 score of ≥ 35.
The presumption based on available data is that PCA3 is prostate cancer specific and highly over-expressed in men with prostate cancer. The clear implication is that a high PCA3 score should result in a high positive predictive value (PPV) and high specificity for a positive biopsy. But things may not be that simple.
Roobol et al. set out to re-test men who had had an initial PCA3 value ≥ 100 and a negative follow-up biopsy and to compare their data to those from a control group who had had an initial PCA3 value < 100 and a negative prostate biopsy. All re-tested patients has PSA and PCA3 values assessed on the basis of blood and urine samples, respectively, and repeat biopsies were performed on all men who had a PSA level ≥ 2.5 ng/ml, a PCA3 score ≥ 35, or both.
The results of this study can be summarized as follows:
The patients were all aged between 63 and 75 years of age.
The average (mean) study period was 19 months.
Prostate cancer was detected on re-biopsy in
The PPV of an initial PCA3 value ≥100 was only 52.2 percent (based on initial and re-biopsy data).
Changes in PSA values and PCA3 values over time were very different in this group of patients.
According to the authors, the PPV and the specificity of the PCA3 data for a positive prostate cancer biopsy in this re-tested group of men with PCA3 scores ≥100 were “comparable” to PPV and specificity values from other series of patients with an initial PCA3 value ≥100. However, … “These findings do not explain why these PCA3 scores were excessively high” even though prostate cancer was undetectable in 100 percent of the patients on a first repeat biopsy and in 70 percent of patients on a second repeat biopsy.
The lesson here is that a very high PCA3 score does not necessarily correlate to a very high probability of a positive biopsy. Although a PCA3 value ≥ 35 is statistically correlated to a significant risk for a positive biopsy in a patient after a first, negative biopsy, there would appear to be at least one subset of patients in whom an elevated PCA3 result may not be indicative of risk for prostate cancer.
The prostate cancer antigen 3 or PCA3 test is already widely used to further assess risk for prostate cancer in a man with a high PSA result (potentially indicative of risk for prostate cancer) but an initial negative biopsy. The “cut point” for re-biopsy is considered to be a PCA3 score of ≥ 35.
The presumption based on available data is that PCA3 is prostate cancer specific and highly over-expressed in men with prostate cancer. The clear implication is that a high PCA3 score should result in a high positive predictive value (PPV) and high specificity for a positive biopsy. But things may not be that simple.
Roobol et al. set out to re-test men who had had an initial PCA3 value ≥ 100 and a negative follow-up biopsy and to compare their data to those from a control group who had had an initial PCA3 value < 100 and a negative prostate biopsy. All re-tested patients has PSA and PCA3 values assessed on the basis of blood and urine samples, respectively, and repeat biopsies were performed on all men who had a PSA level ≥ 2.5 ng/ml, a PCA3 score ≥ 35, or both.
The results of this study can be summarized as follows:
According to the authors, the PPV and the specificity of the PCA3 data for a positive prostate cancer biopsy in this re-tested group of men with PCA3 scores ≥100 were “comparable” to PPV and specificity values from other series of patients with an initial PCA3 value ≥100. However, … “These findings do not explain why these PCA3 scores were excessively high” even though prostate cancer was undetectable in 100 percent of the patients on a first repeat biopsy and in 70 percent of patients on a second repeat biopsy.
The lesson here is that a very high PCA3 score does not necessarily correlate to a very high probability of a positive biopsy. Although a PCA3 value ≥ 35 is statistically correlated to a significant risk for a positive biopsy in a patient after a first, negative biopsy, there would appear to be at least one subset of patients in whom an elevated PCA3 result may not be indicative of risk for prostate cancer.