Wednesday May 13 2009
Prostate cancer is the most common cancer in men
“Scientists are closer to developing a more accurate test for prostate cancer which could save hundreds from surgery every year,” reported the Daily Mail. It said that a urine test could identify those who need further treatment and those whose cancer is dormant. The newspaper continued that, “tiny globules of fat in men's urine contain RNA molecules which could indicate whether the cancer is aggressive”.
This study involved the analysis of genetic material shed by tumour cells and excreted in the urine of men with prostate cancer. The researchers were able to detect two cancer biomarkers: PCA-3 and TMPRSS2:ERG. These markers are potentially more accurate diagnostic markers for prostate cancer. They also offer an easier, non-invasive alternative to the prostate specific antigen (PSA) blood test. However, this research is in its very early stages and this small pilot study involved testing samples from only 11 cancer patients. In addition, the diagnostic accuracy of the test for detecting new cases or aggressive cases has not been studied. As such, further research is anticipated.
Where did the story come from?
This research was carried out by J Nilsson from the Department of Radiation Sciences, Umea University, Sweden and colleagues from other institutions in The Netherlands and Harvard Medical School in the US. The work was supported by grants from the Swedish Cancer Research Foundation, Wenner-Gren Foundation, Stiftelsen Olle Engkvist Byggmastare, National Cancer Institute (NCI) and the Lions Research Foundation, Umea University, Sweden. The study was published in the peer-reviewed British Journal of Cancer.
What kind of scientific study was this?
In this experimental pilot study, the authors investigated a new approach for the diagnosis of prostate cancer.
Currently, the main test for prostate cancer is the PSA test, which looks for raised levels of prostate specific antigen (PSA) in the blood. Prostate cancer increases the production of PSA, so the test may be able to detect prostate cancer in its early stages. The PSA test is established as a reasonably sensitive test for detecting cancer and it is useful for predicting response to treatment.
However, the test is limited in that it produces false positives, meaning it can give a positive result when there is no cancer. This is because benign conditions, such as enlarged prostate, are also associated with raised PSA levels. Also, the PSA test does not distinguish between aggressive cancers, which spread quickly and are life threatening, and less aggressive cancers, which may never spread beyond the prostate.
The authors say that additional prostate cancer markers are needed, especially those that can predict severity of the disease and the likelihood that the cancer will spread to other areas of the body. This study investigated how prostate cancer might be detected by the presence of certain waste products expelled by tumour cells. This involved looking at the transcriptome (the messenger RNA that shows the genetic make-up of the cell) within exosomes. These are small fat-containing vesicles (fluid-filled bubbles) that are involved in the removal of cell membrane proteins from within the cell.
The researchers collected urine samples from 11 prostate cancer patients. Of these, four were untreated, two treated medically or surgically, three had cancer spread to the bone and samples of two were examined using electron microscopy (to confirm the presence of exosomes in the urine). The patients were at various stages of their cancer (determined by cancer grade, Gleason score and PSA level). Samples were detected before and after performing mild prostate massage (massage was not performed in those with bone cancer spread).
What were the results of the study?
The researchers detected two prostate cancer biomarkers, PCA-3 and TMPRSS2:ERG, in the exosomes. Neither of the markers was detected in the urine of treated patients and those with cancer spread to the bone. However, after prostate massage, PCA-3 was detected in the urine of all four of the untreated prostate cancer patients. TMPRSS2:ERG was only detected in the two untreated patients, who were at a slightly more advanced stage of their prostate cancer than the other two. The patients analysed by electron microscopy did not have their levels analysed.
PSA was also expressed in the urine exosomes of the four untreated men, but only after they had received mild prostate massage, indicating that this was necessary to increase exosomal excretion into the urethra and the urine.
What interpretations did the researchers draw from these results?
In their study, as ‘proof-of-concept’, they demonstrated that there are two prostate cancer biomarkers, PCA-3 and TMPRSS2:ERG, in the exosomes found in patients’ urine. This, they say, shows the potential for urine testing in diagnosing and monitoring cancer patients’ status.
What does the NHS Knowledge Service make of this study?
This research involved the analysis of genetic material shed from within tumour cells and excreted in the urine of men with prostate cancer. Using laboratory methods the researchers demonstrated that tumour exosomes in the urine carry genetic information specific to prostate cancer. Specifically, they were able to detect two cancer biomarkers, PCA-3 and TMPRSS2:ERG. The researchers say their study suggests that, potentially, these could be more accurate diagnostic markers for prostate cancer and an alternative to the PSA blood test. A urine test would also have the advantage of being an easy, quick and non-invasive test.
However, this research is in its very early stages and this small pilot study involved testing samples from only 11 cancer patients. In addition, the diagnostic accuracy of the test for detecting new cases or aggressive cases has not been studied. As such, further research is anticipated.