Merging digital rectal exam, family history, age and prostate-specific antigen to create a decision-making tool

In this paper, we report on risk factors for prostate cancer detection on biopsy as found in the Prostate Cancer Prevention Trial (PCPT), with special emphasis on the independent contribution of prostate-specific antigen (PSA) velocity to prostate cancer risk over that provided by PSA. For this study, we used a subset of PCPT placebo arm participants who had had at least one prostate biopsy and a digital rectal examination (DRE) and PSA measured within 1 year prior to biopsy. In order to evaluate PSA velocity, we also required an additional PSA measurement within 3 years prior to biopsy, yielding 5,519 PCPT placebo arm participants for inclusion in the analysis. The risk of prostate cancer rose from 11.1% for PSA values less than 1 ng/mL to 43.3% for PSA values greater than 6 ng/mL and the risk of high-grade disease rose from 1.0% to 22.0% across these two PSA intervals. It was in fact no longer statistically significant as soon as the single predictor PSA was added to the risk equation, whereas PSA remained statistically significant even when velocity was in the risk equation. Furthermore, in a head-to-head comparison of predictive strength as a single predictor in a model, assessed by maximized log likelihood, PSA was more predictive than PSA velocity. These findings occurred for every definition of velocity that was considered and hence we concluded that velocity did not add independent prognostic information to prostate cancer risk over that provided by PSA. Similarly, age, which is also a predictor of prostate cancer in the absence of other factors, did not add independent prognostic information to PSA, DRE, family history, and prior biopsy.