UPDATE - Issue 19 - October 2004
PSA not worthless
says Professor Roger Kirby
You may have seen a flurry of headlines recently along the lines that the PSA test is worthless. Such irresponsible reporting appears to stem from a recent article published by Professor Tom Stamey who undertook much of the early work on Prostate Specific Antigen (PSA) testing for prostate cancer. His original work demonstrated that the PSA value in the bloodstream correlated rather well with the size and grade of the cancer removed at subsequent radical prostatectomy. His recent analysis of patients operated on over the last five years shows that this close correlation has been lost. Furthermore, another study reported by Dr Ian Thompson has shown that prostate cancer occurs in up to 17% of men who have a PSA less than 4.0ng/ml. In fact, these data come as no surprise to those of us who have used this blood test very extensively for the last decade and a half. We have long known that there is no precise relationship between the size of the tumour and the preoperative value of PSA and we have also been aware that PSA provides very limited information about how aggressive an individual cancer is likely to be. What PSA is able to tell us is whether or not something is amiss within the prostate and therefore who should and who should not undergo a prostate biopsy. The biopsy itself will confirm the presence of cancer and also give us important clues about the grade of that tumour. This in turn provides information about how likely the cancer is to progress and eventually spread.
certainly not yet at the end of the PSA era
New markers, such as the uPM3 (sometimes known as PCA3) urine based genetic test seem to be asignificant advance in the detection of prostate cancer. This gene is expressed 43 times more vigorously in cancerous compared with benign prostate cells. Other molecular markers also seem likely to provide a better indicator than the Gleason score of how the tumour is likely to behave, and therefore whether the patient should be treated by active surveillance or more radical treatment such as prostatectomy or radiotherapy. More research is, however, needed before these can replace the current testing methods.
While PSA may eventually be surpassed as a diagnostic and screening tool, its value in monitoring the response to either surgery, radiotherapy or hormone therapy is likely to remain pivotal for the foreseeable future. It is also increasingly used as a means of estimating prostate size in patients with benign prostatic hyperplasia (BPH) and also is of value in selecting which type of medical therapy an individual patient is most likely to respond to.
In conclusion, contrary to Professor Stamey's suggestion, we are certainly not yet at the end of the PSA era. However we are at the beginning of what promises to be a bright new future. New, more sophisticated molecular tests will soon be available to give us important information about the way individual cancers in the prostate are likely to behave. This should eventually improve the outcome for the very many sufferers of all forms of prostate disease.