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Diagnosis of prostate cancer has relied heavily on serum Prostate Specific Antigen (PSA), physical examination by digital rectal examination (DRE) and biopsy. However all have shortcomings. Non-malignant conditions (eg prostatitis and benign prostatic hyperplasia) can cause PSA levels to rise and the positive predictive value (PPV) for diagnosing cancer by serum PSA is low. Approximately 75% of men suspected of having cancer based on PSA testing actually have non-cancerous conditions. The PPV by DRE is even lower (10%). Complications caused by prostate biopsy are well documented. As many as 10 – 25% of patients with a negative biopsy may have prostate cancer.
PCA3 is prostate cancer specific, over expressed in >95% of malignant tissue, and is significantly up-regulated (60-100 fold) in prostate cancer. PCA3 is more prostate cancer specific than PSA with a positive predictive value to diagnose prostate cancer being almost twice than of serum PSA. PCA3 is only expressed in prostate tumour – not in benign or normal tissue and is not affected by the size of the prostate.
Testing for PCA3 is from a urine sample. The urine sample must be collected following a DRE. The released prostate cells are collected in a first catch urine after the DRE. Gen-Probe urine sample collection tubes must be used and there are important storage and temperature instructions once the urine sample has been collected. The PCA3 result is reported as a score; the higher the score the greater the probability of a positive prostate biopsy whilst the lower the score the likelihood of a positive biopsy decreases. The greatest diagnostic utility occurs at a cut off of 35.
By measuring the expression of mRNA from the PCA3 gene, this new assay provides greater accuracy: a positive result may indicate prostate cancer and the need for an additional biopsy; a negative result even though accompanied by a PSA greater than 4 ng/ml suggests a relatively longer time interval may be acceptable between biopsies.
The routine use of PCA3 in men with raised PSA levels with negative biopsies would expect to both enhance the early detection of cancer in these men, as well as reduce the number of unnecessary biopsies. The use of PCA3 in combination with current PSA testing and increased accuracy for timing of biopsies would also increase the biopsy yield of positive cancers (UROLOGY.2007;69:532 – 535).
For further information about PCA3, or to order Gen-Probe PCA3 Urine Specimen Transport Tubes please contact Annette Wilkinson or Lynn Derby-Lewis at The Doctors Laboratory on 020 7307 7373 or by email firstname.lastname@example.org.
As the PCA3 score increases the likelihood for positive biopsy increases. As the PCA3 score decreases, the likelihood for a positive biopsy decreases. The greatest diagnostic utility occurs at a cut-off of 35.
Sample Information - See TDL Laboratory Guide page 56 (Tumour Markers)
|Test||Code||Sample Type||Turnaround Time|
|PCA3||PCA3||1 x Gen Probe PCA3 Sample Transport Tube||5-7 working days|
|DRE and Urine sample collection is by appointment (020 7307 7383) at Patient Reception, 55 Wimpole Street, London W1G 8YL|