The PCA3 test is a relatively new way of assessing prostate cancer risk, introduced in the UK in 2007.
It is based on using genetic technology to assess prostate cancer risk and therefore works in a different way to the standard PSA test. PCA3 is short for Prostate Cancer gene 3.
The PCA3 test is only undertaken by urologists specialising in the assessment and treatment of prostate cancer. The prostate is examined by a urologist during a digital rectal examination (DRE) and the PCA3 test uses the first urine passed after this procedure. The urine is tested for the genetic marker, PCA3 mRNA concentration which is used to calculate a PCA3 score. The higher the PCA3 score, the more likely it is that cancer is present.
When the level of PCA3 is high, it leaks into the urine. Up to 100 times more PCA3 is present in prostate cancer cells than non-cancerous cells.
Like the PSA test, the PCA3 is not absolute - it does not definitely indicate whether or not you have prostate cancer. It gives you and your urologist a risk assessment of how likely you are to have the disease. This table shows how PCA3 results are measured and understood:
PCA3 Score Probability of Prostate Cancer on Biopsy
The advantage of the PCA3 test is that it measures prostate cancer risk in a different way to the PSA test and therefore provides urologists with extra information to understand individual risk.
This is important because prostate cancer risk is difficult to assess. The PSA test is an imperfect assessment tool, based on measuring a protein called the Prostate Specific Antigen (PSA) within the blood.
The PSA is made by the prostate and naturally leaks into the bloodstream when the prostate is damaged and therefore a high level of PSA can indicate prostate cancer may be present. However, a high PSA result can also be caused by non-cancerous conditions, such as an enlarged prostate, known medically as Benign Prostatic Hyperplasia (BPH). This is because a large prostate will simply produce more PSA and high levels are a result of prostate volume, rather than disease.
Equally, many men have a slightly raised PSA result, which does not give a clear indication of cancer being present and it is difficult to judge whether a biopsy is necessary. For these patients, the PCA3 test adds another level of important information to help make that judgment.
Unlike the PSA test, the PCA3 score is not affected by the size of the prostate. The PCA3 test is also less affected by urinary infections, which can make the PSA completely unreliable.
While the PCA3 test is significantly better than PSA alone, it is not a 'miracle' single answer to the complexities of assessing risk of prostate cancer. The PCA3 test must be used not only with the PSA, but also in conjunction with digital rectal examination findings, age, family history, transrectal ultrasound and prostate size.
Combined with this range of assessment tools, the PCA3 test represents an important new diagnostic tool in the wider armory of assessments used to measure individual prostate cancer risk.