|
The cPSA test outperforms the tPSA test in specificity and positive predictive value |
|
|
|
27 Apr 2006 |
LEVERKUSEN, Germany | Apr 26, 2006 | Determination of complexed prostate-specific antigen (cPSA) has been shown to outperform tPSA testing (total PSA) which has been the method of choice up to date. The cPSA test marketed by the Diagnostics Division of Bayer HealthCare AG detected patients with a more than twofold higher risk for prostate cancer from among a population of patients with inconsistent (discordant) results in both tests; the specificity of the cPSA test was between 3.6 and 5.5 times greater than that of the tPSA test. Using the cPSA test instead of the tPSA test could eliminate the need for over ten percent of the prostate biopsies performed unnecessarily in patients in the tPSA range between 3 and 5 ng/ml. These findings were published in the April 2006 issue of the renowned Journal of Urology (Klaus Jung et al., Vol. 175 (4), 1275-1280, April 2006).
The study evaluated data from two studies of prostate cancer involving a total of 1,624 individuals, among them 776 who did not have prostate cancer. The study used the new DAC (discordance analysis characteristics) method to analyze PSA concentrations only for those patients who had inconsistent results in the two tests. A further study (Clinical Chemistry, Vol. 51 (3), 532-539, 2005) has shown that DAC avoids the severe biases associated with commonly used ROC (receiver operating characteristics) analysis when the sample selection is based on one test only (tPSA); DAC therefore correctly shows the superior diagnostic performance of a test.
The new study shows that a patient with elevated cPSA but normal tPSA has a roughly twofold greater probability of having prostate cancer than a man with elevated tPSA and normal cPSA. In clinical practice this means that the cPSA test is better at pre-selecting patients for a potential prostate biopsy. The authors of the study therefore recommend that cPSA should be used as the initial diagnostic test for detecting prostate carcinoma.
The analysis also showed that patients with a positive tPSA test and a negative cPSA test often do not have prostate cancer suggesting that the tPSA test is less specific. In this context, the specificity of each test correlates directly with the number of biopsies that could potentially be avoided. This is why using the cPSA test should lead to fewer unnecessary biopsies.
The study found that with a tPSA cut-off value of 4 ng/ml there was a considerable increase in the number of patients who benefited from cPSA determination. More than ten percent of biopsies could be eliminated by using the cPSA test instead of the tPSA test. As the authors note, this may be highly significant in practice, as nowadays a prostate biopsy may be considered even for patients whose tPSA is below 4 ng/ml.
Total PSA (tPSA) is made up of bound (complexed) cPSA and an unbound proportion of free PSA (fPSA). Elevated levels of cPSA are found particularly in the blood of patients with prostate cancer. Free PSA, on the other hand, is excreted in greater quantities by patients with benign prostate conditions. cPSA concentrations are measured using the fully automated ADVIA Centaur® immunology system from Bayer HealthCare.
Prostate cancer is the most common form of cancer in men, with some 40,000 individuals being diagnosed with it in Germany every year. According to the World Health Report 2004 the WHO estimated 269.000 deaths by prostate cancer worldwide. PSA, and more particularly cPSA, is the most important tumor marker for early detection. If prostate cancer is detected at an early stage, patients can very often be cured by appropriate therapy.
Bayer HealthCare
Bayer HealthCare, a subsidiary of Bayer AG, is one of the world’s leading, innovative companies in the health care and medical products industry based in Leverkusen/Germany. In 2005, the Bayer HealthCare subgroup generated sales amounting to some 9.4 billion Euro. Bayer HealthCare employed 33.800 people worldwide in 2005.
The company combines the global activities of the divisions Animal Health, Consumer Care, Diabetes Care, Diagnostics and Pharmaceuticals. Since January 1, 2006 the new Pharmaceutical Division consists of the former Biological Products and Pharmaceutical Division and now comprises three business units: Hematology/Cardiology, Oncology and Primary Care.
Bayer HealthCare’s aim is to discover and manufacture products that will improve human and animal health worldwide. The products enhance well-being and quality of life by diagnosing, preventing and treating diseases.
SOURCE: Bayer |
