UPDATE - Issue 40 - Spring 2010
PCA3 urine test predicts prostate cancer biopsy results
An initial analysis of more than 1,000 patients found that a urine-based test for prostate cancer gene 3 (PCA3) could accurately predict the results of a prostate biopsy. Results confirm earlier small trials suggesting that PCA3 is more predictive of prostate biopsy results than standard prostate specific antigen (PSA) testing, claimed researchers at the 2010 Genitourinary Cancers Symposium in San Francisco, USA.
'PCA3 is over expressed in 95% of all prostate cancers by 60 to 100 fold compared with normal tissue,' said Leonard Marks of University of California, Los Angeles. 'These results confirm that PCA3 is more closely associated with prostate cancer than PSA is.'
Researchers evaluated PCA3 among 1,140 men in the placebo arm of the four year Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial to test the use of dutasteride to reduce risk for prostate cancer. The placebo arm was used because the men entered the trial with negative prostate biopsies and were already scheduled for repeat 10-core biopsies at years two and four.
During the trial, urine specimens were collected immediately following digital rectal examination, frozen, and analysed at a central lab. The resulting PCA3 score was significantly correlated with a positive prostate biopsy result. Among men with a PCA3 score of less than 5, only 6% had a positive prostate cancer diagnosis; among men with a PCA3 score of more than 100, 57% were diagnosed with cancer. Higher PCA3 scores also correlated with more aggressive cancers. In addition, PCA3 at year two was correlated with positive biopsy results at year four. These results are similar to the results of earlier and smaller trials.
'A very low score gave a very low risk for prostate cancer and a high score was very indicative of cancer,' Marks said. 'In practical terms, this tells us that even if a biopsy is negative, a high score means that there is probably a tumour that we missed.'
He also said that the appropriate cut off appears to be 35. That level provides a useful combination of 58% sensitivity and 72% specificity. PCA3 levels are not affected by BPH or prostatitis, both of which can elevate PSA levels.