In the news

BBC News Online has reported the launch of a gene expression test that could improve the accuracy of the diagnosis of prostate cancer. Currently, a blood test is available that detects raised levels of a protein called prostate serum antigen (PSA); men with a high PSA score may be offered a prostate biopsy to determine whether cancerous cells are present in the prostate. The problem is that the PSA test has relatively poor specificity and positive predictive value, limiting its clinical value. For every 100 men with elevated blood levels of PSA, only about 30 subsequently have a positive biopsy. Management of these patients is then difficult, as they may have to undergo repeated painful and distressing biopsies despite never developing the disease.

A company called Gen-Probe has developed a more accurate, non-invasive test based on measuring expression levels of a gene called PCA3 in a urine sample. The PCA3 gene is over-expressed in about 95% of prostate cancers. The Progensa PCA3 test reportedly has substantially better specificity and positive predictive values than the PSA test but, at £200 per test compared with £10 for the PSA test, is unlikely to be adopted for routine use in the NHS. A Horizon Scanning Technology Briefing Paper produced by the National Horizon Scanning Centre at the University of Birmingham in December 2006 summarises the characteristics of the PCA3 test and suggests that it may prove useful in men who have raised PSA levels but a negative prostate biopsy (thus potentially sparing them repeated biopsies) or in men with slightly raised PSA levels or other clinical symptoms that suggest the possibility of prostate cancer.