Nomogram predicting the outcome of salvage radiation therapy for prostate-specific antigen failure following radical prostatectomy: an exploratory analysis of a randomized, multicenter, open-label, phase 3 trial (JCOG0401)

Background: We have demonstrated that patients with prostate-specific antigen failure following radical prostatectomy benefit from salvage radiation therapy prior to salvage hormone therapy in a multicenter, randomized, open-label, phase 3 trial (JCOG0401). This study aimed to develop a nomogram to predict the efficacy of salvage radiation therapy in patients with prostate-specific antigen failure following radical prostatectomy. Methods: This exploratory study focused on the salvage radiation therapy arm of the JCOG0401 trial and explored clinical factors that were significantly associated with the time to treatment failure of salvage radiation therapy using univariable and multivariable analyses. Based on these factors, we developed a nomogram to predict 3- and 5-year time to treatment failure. Discrimination and calibration of the nomogram were performed using concordance statistics and calibration plots. Results: Ninety-six patients were included in the analysis, with a median time to treatment failure of 4.7 years. Multivariable Cox regression analysis identified pathological T stage ≥ 3, lack of lymph node dissection, lack of nerve-sparing, and prostate-specific antigen-doubling time < 6 months as significant factors associated with time to treatment failure (P < 0.05 for each). The nomogram including these factors achieved a concordance statistics of 0.6996. The hazard ratio for time to treatment failure was 2.946 (95% confidence interval 1.624–5.347), when the cut-off value of the nomogram was determined as the median nomogram score. Conclusions: The developed nomogram enables moderate prediction of the efficacy of salvage radiation therapy in patients with prostate-specific antigen recurrence following radical prostatectomy.