Clinical Services

Prostate Cancer Gene 3 (PCA3) Assay

The use of the serum prostate-specific antigen (PSA) test for prostate cancer screening has resulted in the biopsy diagnosis of smaller, previously undetected tumors,1 thus creating a new diagnostic dilemma: Only a fraction of men with increased serum PSA levels have detectable prostate cancer. Men with at least one negative biopsy often have persistently increased serum PSA, due primarily to enlarged prostates and benign prostatic hyperplasia (BPH). Yet, a significant proportion of men with slightly increased serum PSA (2.5-4.0 ng/L) either have, or will develop, clinically significant prostate cancer.1 While biopsy remains the gold standard for prostate cancer detection, more accurate tests with better specificity are needed to help guide decisions to biopsy the prostate.

Introduction to PCA3

PCA3 (also known as "PCA3DD3" or "DD3PCA3") is a non-coding prostate specific mRNA that is highly over-expressed in prostate cancer cells, with a median 66-fold up-regulation compared to adjacent benign tissue.2 In contrast, PSA gene expression is similar in cancerous and benign cells; PSA mRNA levels may therefore be used to normalize for the amount of prostate-specific ribonucleic acid (RNA) in molecular test samples. The feasibility of quantitative PCA3-based molecular testing from urine sediments2 and from whole urine3 has been demonstrated.

The Prostate Cancer Gene 3 (PCA3) Assay utilizes whole urine collected following a digital rectal examination (DRE) consisting of three strokes per lobe (Figure 1). The DRE releases prostate cells through the prostate duct system into the urinary tract, where they can be collected in the first catch urine. The urine is processed by addition of Urine Transport Medium (UTM), which lyses the cells and stabilizes the RNA. PCA3 and PSA mRNAs are quantified, and the PCA3 Score is determined based on the ratio of PCA3/PSA mRNA. In addition to normalizing PCA3 signal, measurement of PSA mRNA also serves to confirm that the yield of prostate-specific RNA is sufficient to generate a valid result. Higher PCA3 Scores correlate with higher probability of a positive prostate biopsy.

Figure 1

Figure 1.  PCA3 assay sample collection procedure.

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PCA3 Score is Independent of Prostate Volume

In 570 American men scheduled for (initial or repeat) biopsy4, it was assessed whether or not the PCA3 Score was influenced by prostate volume. Prostate volume data were available for 552 men.

As expected, the median serum PSA level increased with prostate volume (P < 0.0001). Men with a prostate volume of < 30 mL, 30-50 mL and > 50 mL had a median PSA level of 4.8, 5.4 and 7.0 ng/mL, respectively. In contrast, the median PCA3 Score did not increase with prostate volume (P = 0.54). The PCA3 Score was 25, 21 and 23 in men with a prostate volume < 30, 30-50 and > 50 mL, respectively (Figure 2). These results provide indirect proof for the fact that the PCA3 Score is, in contrast to serum PSA, highly prostate cancer specific.

Figure 2

Figure 2.  Relationship between prostate volume and total PSA or PCA3 score.

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Interpreting the PCA3 Score for Making Better Biopsy Decisions

Several clinical studies have evaluated the use of the PCA3 Score in aiding the decision whether or not to biopsy. These studies included men who had their first biopsy and men scheduled for repeat biopsy.

US data, first biopsy5

  • In 260 American men (mean serum PSA ~8 ng/mL) who were scheduled for a first biopsy, the PCA3 score was determined and related to prostate biopsy outcome.
  • In total, 111 men (43%) had a positive biopsy.
  • The percentage of men with a positive biopsy increased with the PCA3 score.
  • A PCA3 score cut-off of 35 provided the greatest diagnostic accuracy, i.e., balance between sensitivity (50%) and specificity (77%).
  • Men with a PCA3 score >= 35 had a 2-fold increased risk of a positive biopsy compared to those with a PCA3 score < 35 (Figure).
  • Men with a PCA3 Score >= 35 had a 62% probability of a positive biopsy; in other words about 2 in 3 men with a PCA3 score >= 35 had prostate cancer (Figure 3).

US data, repeat biopsy6

  1. 1. Another study involved 233 American men (mean serum PSA 7.4 ng/mL) who had had at least 1 negative previous biopsy and were scheduled for repeat biopsy.
  2. 2. The PCA3 score was also determined and related to prostate biopsy outcome..
  3. In total, 60 men (27%) had a positive biopsy.
  4. The percentage of men with a positive biopsy increased with the PCA3 score.
  5. A PCA3 score cut-off of 35 provided the greatest diagnostic accuracy, i.e., balance between sensitivity (58%) and specificity (72%).
  6. Men with a PCA3 score >= 35 had a 2.5-fold increased risk of a positive biopsy compared to those with a PCA3 score < 35 (Figure 4).
  7. Men with a PCA3 score >= 35 had a 43% probability of a positive biopsy; in other words almost 1 in 2 men with a PCA3 score >= 35 had prostate cancer (Figure 3).

European data, repeat biopsy7

  • In a preliminary analysis, 199 European men (mean serum PSA 8.2 ng/mL) had had 1-2 previous negative biopsies and were scheduled for repeat biopsy. In these men, the PCA3 score was also determined and related to prostate biopsy outcome.
  • The results were very consistent with the US data.
  • In total, 49 men (25%) had a positive biopsy..
  • The percentage of men with a positive biopsy increased with the PCA3 score.
  • A PCA3 score cut-off of 35 provided the greatest diagnostic accuracy, i.e., balance between sensitivity (57%) and specificity (73%).
  • Men with a PCA3 score >= 35 had a 2.5-fold increased risk of a positive biopsy compared to those with a PCA3 score < 35 (Figure 4).
  • Men with a PCA3 score >= 35 had a 41% probability of a positive biopsy; in other words almost 1 in 2 men with a PCA3 Score >= 35 had prostate cancer (Figure 3).

Figure 3

Figure 3.  Accuracy of PCA3 score in men scheduled for first and repeat prostate biopsy.

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Interpreting the PCA3 Score for Making Better Prognosis Decisions

So far, one study has evaluated if the PCA3 score could be used as an additional test for predicting the prognosis of men diagnosed with prostate cancer.8

  • In this study, 83 men with prostate cancer scheduled for radical prostatectomy also had their PCA3 score measured.
  • The PCA3 score correlated with total tumor volume and tumor grade in prostatectomy specimens.
  • The mean PCA3 score in men with low volume tumors (< 0.5 mL) was significantly lower than in men with intermediate volume (0.5-2.0 mL; P = 0.004) or high volume (>= 2.0 mL; P = 0.002) tumors.
  • The mean PCA3 score in men with low volume (< 0.5 mL) and low grade (Gleason score <= 6) was significantly lower than in men with significant cancers (P = 0.004) (Figure 4).
  • A high PCA3 score seems to be helpful in predicting which men with prostate cancer have a high probability of significant prostate cancer.

Figure 4

Figure 4.  The PCA3 score in significant prostate cancer prostatectomies is significantly higher than in low volume/low grade prostate cancer.

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Clinical Application of the PCA3 Assay

Taking into account the PCA3 research data and how prostate cancer is currently diagnosed in clinical practice, there are several scenarios in which PCA3 may aid in guiding biopsy decisions or provide a useful indication of disease significance.

  1. First, the score can be used to increase confidence in an initial biopsy decision where the serum PSA results are uncertain (2.5-10 ng/mL).
  2. Second, PCA3 testing could be used to increase confidence in a re-biopsy decision, wherein the DRE and serum PSA results are suspicious and/or family history and other factors indicate an increased risk of prostate cancer.
  3. Lastly, when biopsy results are positive but tumor aggressiveness is unknown, PCA3 might be useful in comparing the risks and benefits of radical prostatectomy versus active surveillance management.

Thus, the availability of a PCA3 score alone or combined with existing methods might better guide biopsy decision making than current methods, and might be useful as an indicator of clinical stage and disease significance.

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Ordering

Please contact BioVantra Client Support Center at (866) 301-0960 to arrange for PCA3 testing. Our experienced Client Support Team can assist with:

  • Specialized Testing Requisition
  • Sample requirements
  • Logistics and specimen transportation
  • Testing methodology
  • Report delivery, status or interpretation
  • Expert oncology and pathology consultations
  • Requests for BioVantra literature and scientific references

References

  1. Bussemakers MJ, van Bokhoven A, Verhaegh GW, Smit FP, Karthaus HF, Schalken JA, Debruyne FM, Ru N and Isaacs WB: DD3: a new prostate-specific gene, highly overexpressed in prostate cancer. Cancer Res. 59: 5975-9, 1999.
  2. Hessels D, Klein Gunnewiek JM, van Oort I, Karthaus HF, van Leenders GJ, van Balken B, Kiemeney LA, Witjes JA and Schalken JA: DD3(PCA3)-based molecular urine analysis for the diagnosis of prostate cancer. Eur Urol. 44: 8-15; discussion 15-6, 2003.
  3. Groskopf J, Aubin SM, Deras IL, Blase A, Bodrug S, Clark C, Brentano S, Mathis J, Pham J, Meyer T et al.: APTIMA PCA3 molecular urine test: development of a method to aid in the diagnosis of prostate cancer. Clin Chem. 52: 1089-95, 2006.
  4. Deras IL, Aubin SM, Blase A, Day JR, Koo S, Partin AW, Ellis WJ, Marks LS, Fradet Y, Rittenhouse H et al.: PCA3: a molecular urine assay for predicting prostate biopsy outcome. J Urol. 179: 1587-92, 2008.
  5. Gen-Probe: Data on file, 2007.
  6. Marks LS, Fradet Y, Deras IL, Blase A, Mathis J, Aubin SM, Cancio AT, Desaulniers M, Ellis WJ, Rittenhouse H et al.: PCA3 molecular urine assay for prostate cancer in men undergoing repeat biopsy. Urology. 69: 532-5, 2007.
  7. Haese A, Van Poppel H and Marberger M: The value of the PCA3 assay in guiding decision which men with a negative prostate biopsy need immediate repeat biopsy: preliminary European data. Eur Urol Suppl. 6 abs. 101: 48, 2007.
  8. Nakanishi H, Groskopf J and Bhadkamkar V: The relationship between PCA3 score and tumor volume in prostatectomy samples. J Clin Oncol. abs., 2007.

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