How reliable is the PCA3 test for prostate cancer?

Mr Alan Doherty

How reliable is the PCA3 test for prostate cancer? What we have learnt from undertaking 688 tests

By Alan Doherty

Back in 2007, we were one of the first clinics in the UK to introduce a new type of test for prostate cancer. This test was based on the discovery that very high levels of a gene called PCA3 are expressed when cancer is present in the prostate. When this is the case, prostate cells that contain PCA3 leak into the urine, thus providing a new ‘biomarker’ for the disease.

The results of the PCA3 test are expressed as follows: the patient is given a PCA3 score and any score above 25 is considered “positive” showing a significant risk of prostate cancer.

The weakness of the PCA3 test is immediately apparent: there is a broad scale and only an approximation of risk. As such, the PCA3 test was never intended to be a stand-alone assessment nor a replacement for the widely used PSA (prostate specific antigen) test.

However, we decided to introduce the PCA3 test because it offers a different layer of information in addition to the PSA and the other tests we undertake (MRI, DRE). The test is looking to measure a different expression to the PSA and it is more cancer specific. The PCA3 result is much less likely to be affected if a man has a larger prostate volume, commonly due to benign prostatic hyperplasia (BPH)

We really see the value of the PCA3 test combined with the PSA in “quandary” scenarios (where results are on the borderline of age-related thresholds, i.e. score of between three and ten). These would be, for example, a man whose PSA is within the age-related threshold but who has other risk factors such as family history, or equally, a man whose PSA is slightly raised but whose digital rectal examination is normal. The extra ‘piece of the jigsaw’ provided by the PCA3 test is extremely valuable in quandary scenarios when we are judging whether to progress to biopsy.

Our experience tells us that with a PCA3 score of more than 25, I will always proceed to biopsy, even if other indicators (such as MRI or PSA), suggest low risk because the PCA3 is highly specific to the presence of prostate cancer.

We recognise that with such a high volume of PCA3 results from the past eight years, together with records of subsequent investigations and decisions, at BPC we have a valuable research resource. We know exactly how PCA3 results fit into the bigger picture of the different assessments we use to evaluate risk, but we are now embarking on a formal study to precisely measure what contribution PCA3 makes to the process of diagnosing prostate cancer.