Risk factors for disease progression after post-prostatectomy salvage radiation: Long-term results of a large institutional experience.

Abstract

110 Background: Salvage radiotherapy (SRT) has been successfully used to treat recurrent prostate cancer following radical prostatectomy (RP). The objective of this study was to identify risk factors for disease progression post-SRT. Methods: Retrospective review of 719 consecutive patients who had RP and received post-operative radiation (adjuvant/SRT) for recurrent prostate cancer from 1992-2013. Disease progression was defined by a prostate specific antigen (PSA) ≥0.2 ng/ml, local recurrence, nodal failure, or distant metastases. Analysis was restricted to patients treated after 2000, when the PSA detectability threshold decreased to 0.2. Univariable and multivariable Cox regression analysis with backwards selection was performed with the following variables: demographics (age, race), pathological features (Gleason score, positive margins, pT-stage), surgery type, radiation details, hormone therapy, and pre-SRT PSA. Secondarily, we included PSA velocity and doubling-time as continuous variables in the model. Results: 384 patients received SRT after 2000, of which 152 had disease progression, with a median time to recurrence of 6.2 years (95% CI 4.1-7.6 years). Multivariable analysis results are reported in the Table. Gleason score, T-stage, seminal vesicle invasion, and pre-SRT PSA were associated with progression. Pre-SRT PSA ≤ 0.3 conferred the lowest rate of disease progression. In a secondary model, PSA kinetics was evaluated in which doubling-time was associated with progression (HR 0.98 per month increase, 95% CI 0.96-1.00; p=0.03). Conclusions: The lowest rate of disease progression was found amongst patients treated with a PSA ≤ 0.3. A shorter DT may also be a useful predictor of disease progression after SRT. [Table: see text]