New urine-based test may be able to eliminate need for biopsy in many patients

A new report giving preliminary data on the clinical performance of novel, urine-based prostate cancer assay uses a method known as prostate-specific antigen/solvent interaction analysis (PSA/SIA) to detect the ratios of different types of PSA (PSA “isoforms”) in the urine of men beleived to be at risk for prostate cancer.

Stovsky et al. studied data from 222 men scheduled for a prostate biopsy (based on “standard” clinical criteria for risk of prostate cancer) at three clinical centers in Cleveland, OH. Prior to being given a transrectal ultrasound (TRUS)-guided biopsy, these patients were all asked to undergo a digital rectal examination with systematic prostate massage followed by collection of urine.

The urine collected then underwent a PSA/SIA assay designed to determined the relative partitioning of heterogeneous PSA isoform populations between two different aqueous (“water-based”) solvents. A structural index, k, whose numerical value is defined as the ratio of the concentration of all PSA isoforms, was calculated and was then used to set a diagnostic threshold for prostate cancer.

After the patients had been biopsied, their biopsy specimens were pathologically classified as either cases (malignant, n = 100) or controls (benign, n = 122).

Comparison of the available data for the cases and the controls then showed the following results:

  • At a cutoff value of k = 1.73, PSA/SIA displayed
    • A sensitivity of 100 percent
    • A specificity of 80.3 percent
    • A positive predictive value (for the presence of prostate cancer) of 80.6 percent
    • A negative predictive value (for the absence of prostate cancer) of  100 percent

The authors made no attempt (at this stage) to further control patient population or the selection criteria for biopsy. They also made no attempt to investigate the structural differences in PSA isoforms that led to changes in the k value.

Although these data and the test methodology will need further close analysis and independent replication before this procedure could possibly be considered as a commercially valuable test for risk of prostate cancer, what is interesting is that this test appears to have a far higher level of specificity and sensitivity than the standard PSA test, most particularly as a means to identify men who would have a negative biopsy. It is possible that this test could be developed commercially as a tool to rule out the need for biopsies for tens or even hundreds of thousands of men currently undergoing unnecessary biopsies each year and getting negative results.

2 Responses

  1. Should this test be used for screening? With 100% sensitivity and 80% specificity, it would probably be a good tool for screening.

  2. Reuven … I don’t think this test is anywhere near ready for “prime time” yet. Let’s see if it can actually do what this preliminary study suggests that it might be able to do before we start to speculate about how to apply it.

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