Prostate cancer
In Italy prostate cancer is the most common cancer in men, accounting for 12% of cases and overtaking lung cancer, which accounts for about 10%. Almost 43,000 cases are recorded in Italy each year, with more than 9,000 deaths (Istituto Superiore di Sanità). About 23,000 new cases are found each year, and 20% of these have already spread. If diagnosed and treated while still confined to the prostate, the cancer is generally curable. These cancers must therefore be detected quickly, before they spread outside the prostate.
Prostate biopsy is an invasive procedure that is currently used to diagnose prostate cancer. Regular screening for this cancer, and therefore the decision to perform a biopsy, is based on measuring PSA (prostate-specific antigen) in the blood, together with a digital rectal examination (DRE). Unfortunately these two tests have limited sensitivity and specificity and a limited positive predictive value (<25-30% and <20% respectively), which makes them difficult to interpret and carries a high risk of false positives and false negatives. This can lead to a late diagnosis or to unnecessary prostate biopsies. There is also a risk of diagnosing latent or slow-growing tumours, with the risk of overtreatment. Moreover, the PSA test gives no information to assess the aggressiveness of the cancer and how dangerous it may be for
the patient.
For these reasons, no scientific or medical association currently recommends routine screening for prostate cancer with PSA and DRE.
The PCA3 gene
PCA3 is a gene specific to prostate cancer. Expression of PCA3 messenger RNA (mRNA) is increased 60 to 100 times in 95% of prostate cancers compared with normal prostate cells.
PCA3 is independent of prostate volume, inflammation, serum PSA and the number of biopsies already performed.
The PCA3 test
The test (Progensa™ PCA3 assay by Gen-Probe) is highly specific and uses an amplification method to quantify both PCA3 mRNA and PSA mRNA in the patient’s urine.
The result provides extremely useful information which, together with the patient’s clinical picture and history, allows an accurate prediction of whether a biopsy is needed.
Advantages of the test:
It provides additional information when deciding on a first biopsy (inconclusive PSA and/or DRE)
It identifies the probability of a positive repeat biopsy in men with a previous negative biopsy, and therefore helps assess whether a new biopsy is needed
It provides information that reduces the patient’s anxiety and avoids unnecessary tests.
How to interpret the test:
As the PCA3 score rises, the probability of a positive biopsy increases, and vice versa.
The greatest diagnostic value appears at a cut-off of 35, with a sensitivity of 57%, a specificity of 73% and a positive predictive value of 68% (the probability that the disease is present when the PCA3 score is ≥ 35).