A comprehensive assessment of the prognostic utility of the Stephenson nomogram for salvage radiation therapy postprostatectomy

Abstract

PurposeTo investigate the prognostic utility of the Stephenson nomogram for clinically relevant endpoints, freedom from metastasis (FFM), and prostate cancer–specific survival (PCSS) in patients treated with salvage external beam radiation therapy (SRT) following a rising prostate-specific antigen (PSA) after radical prostatectomy (RP). Methods and materialsFrom an institutional cohort of 575 patients treated with SRT between 1986 and 2010, the Stephenson nomogram variables were retrospectively collected and available for 179 patients. The prognostic impact of the Stephenson nomogram on 6-year freedom from biochemical failure (FFBF), FFM, and PCSS was assessed on univariate and multivariate analysis using Kaplan-Meier and Cox proportional hazards models. The prognostic utility of the Stephenson nomogram was compared with individual pretreatment, treatment, and clinical characteristics using concordance indices. ResultsIn the 179 patients with all available nomogram variables, median follow-up was 85.0 months (interquartile range [IQR], 53-113) and 6-year FFBF, FFM, and PCSS were 38% (95% confidence interval [CI], 30-46), 79% (95% CI, 73-85), and 96% (95% CI, 92-100), respectively. Univariate analysis, demonstrated that the Stephenson nomogram, as a continuous variable and as a risk stratified group, was prognostic of FFBF (both, P < .0001), FFM (both, P < .0001), and PCSS (both, P ≤ .0005). When analyzing individual Stephenson nomogram variables, multivariate analysis revealed that positive surgical margins (P = .02; hazard ratio [HR], 0.4; 95% CI, 0.2-0.8) and pre-RT PSA (P = .0001; HR, 1.6; 95% CI, 1.3-2.0) were prognostic for FFM, while pre-RT PSA (P = .03; HR, 1.2; 95% CI, 1.0-1.4) was the only prognostic variable for PCSS. Concordance indices revealed the Stephenson nomogram to have superior prognostic capability for biochemical failure (0.71), distant metastasis (0.75), and prostate cancer–specific mortality (0.75) when compared with individual variables (BF all ≤0.65, DM all ≤0.67, PCSM all ≤0.71). ConclusionsFor patients treated with SRT for a rising PSA postprostatectomy, the Stephenson nomogram is an appropriate prognostic tool for estimating the response to treatment; however, there remains a need for improvement in current and future nomograms.