Reliability of prostate-specific antigen-marker in determining biochemical failure during the first 2 years after external beam radiation therapy and hormone therapy in patients with non-operated prostate cancer

Objectives: The presence of prostate-specific antigen (PSA)-bounce after external beam radiation therapy (EBRT) and hormone therapy (HT) makes PSA an unreliable marker in determining PSA biochemical failure (PSA-BF) during the first 2 years after EBRT + HT in patients with non-operated prostate cancer (CaP). To determine the reliability of PSA-BF in predicting clinical outcomes, the Kamat definition, which does not consider PSA-BF during the first 24 months after EBRT, was tested against three other more frequently used methods (American Society of Radiation Oncology, Vancouver, and American Society of Radiation Oncology-Phoenix), which do. Secondly, their relative accuracies in predicting the clinical outcomes were also calculated.

Materials and methods: In January 2011, 193 consecutive CaPs, treated with radical EBRT + HT in our institution from 1999 to 2002, were retrospectively investigated. BF was calculated according to the Kamat definition against the other three above-mentioned methods. Each BF-free survival was analyzed in function of every clinical endpoint (clinical-failure-free survival, cause specific survival, and overall survival) using univariate and multivariate Cox regression analyses. The accuracy of each definition in predicting clinical relapse was also calculated and compared.

Results: Only the Kamat BF definition had both a significant Cox hazard ratio, regarding clinical events or cancer deaths, and the best accuracy values in predicting clinical outcomes. Retrospective study design was the major limitation of the study.

Conclusions: Only the Kamat definition, which does not consider PSA-BF during the first 24 months after EBRT + HT, was shown to be a reliable predictor of clinical events. Thus, our results suggest that solely PSA-based BF should not be considered as a reliable surrogate endpoint during the first 24 months after EBRT + HT. Consequently, caution should be used in adopting rescue treatment without further work-up on an individual basis.