The use of PSA (prostate specific antigen) testing as a strategy to identify men at high risk for prostate cancer is unquestionably successful. However, clinicians report that almost 75% of men who had a positive PSA screen do not have prostate cancer, but rather have benign prostate disease. Furthermore, about 15% of men with a negative PSA screen do have malignant prostate cancer. This inaccuracy is alarming and has led to many unnecessary prostate biopsies. There is a clear need for additional screening methods that sort out the benign from malignant status of men with positive PSA results.

Brian Haab, Ph.D. and colleagues, of the Van Andel Research Institute, have identified several markers that could be utilized when determining the clinical course for men with elevated PSA levels. In the December 27 2006 electronic publication of Prostate, the group reports the use of antibody array profiling--a way to survey the relative abundance of many blood proteins at one time--to develop one high-potency marker that discriminates between benign and malignant prostate disease. Thrombospondin-1 (TSP-1), a protein thought to play many roles in the regulation of immunity and blood cell biology, was identified as the best marker to discriminate between benign and malignant prostate status. Unlike PSA, TSP-1 is found at higher levels in benign samples, but is reduced in biopsy-confirmed malignant samples. This pattern was extremely reproducible and reliable; in about 80% of samples, TSP-1 levels accurately discerned benign from malignant (Shafer et al. 2006 Pros (Epub ahead of print)).

The authors indicate that TSP-1 and PSA testing should be used in combination. PSA levels discriminate healthy patients from those with either benign or malignant prostate disease, but TSP-1 is necessary to then distinguish between benign and malignant disease. The application of both of these prostate markers could reduce the number of false positives that lead to unnecessary biopsies in men with elevated PSA levels.