As usual … the devil is in the details


van den Bergh et al. have conducted a careful investigation of the potential problem caused by the use of different predictive tools for risk of a positive result of prostate biopsy. It is very clear that different nomograms and similar tools can produce divergent outcomes in the same man.

The researchers compared the risk calculators developed on the basis of data from the Prostate Cancer Prevention Trial (PCPT) and the European Randomized Study of Screening for Prostate Cancer (ERSPC). These are two of the largest prospective screening trials conducted to date.

The prediction curves of ‘virtual’ standard study participants were evaluated using both prediction tools within a PSA range of 0.2 to 30.0 ng/mL. The effects of prostate volume, digital rectal examination, transrectal ultrasonography (TRUS), previous negative biopsy, family history, race, and age were also assessed.

The results of their study can be summarized as follows:

  • There are mportant differences in underlying study design and populations between the PCPT and ERSPC which lead to key differences between the predictions offered by the two risk calculators.
  • In the PCPT there were few biopsies in the higher PSA ranges, and in the ERSPC there were few biopsies in the lower PSA ranges.
  • Both risk indicators incorporate some variables that are not used in the other, because they were insignificant in multivariate analysis.
  • TRUS and especially prostate volume (not available in the PCPT) have a considerably larger effect on predictions in comparable PSA ranges than race, age, family history of prostate cancer, and previous negative biopsy (indicators that were excluded in ERSPC).

Not surprisingly, the authors conclude that risk calculators should be applied only after a careful consideration of the relevance of a specific calculator to the individual patient. What were the properties of the underlying populations on which the risk calculator is based? What risk factors are included (or omitted)when using a specific risk calculator?

The “New” Prostate Cancer InfoLink sees this as a fairly straightforward issue in that the risk calculator used to assess the risk of any specific patient should be one that is based on data that reflects that particular patient and his peer group as closely as possible. There is no good reason to use a European-based risk calculator on US patients, or vice versa (at least on the basis of current knowledge).

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