Introduction & Objectives. Salvage radiation therapy (SRT) is a recommended treatment option for biochemical recurrence after radical prostatectomy (RP). However, its effectiveness may be limited to specific categories of patients. We aimed at identifying the optimal candidates for early SRT after RP
Materials & Methods. The study included 925 node-negative patients treated with SRT after RP at seven institutions. Patients received SRT for either PSA rising, or PSA persistence after RP that was defined as PSA level ≥0.1 ng/ml at 1 month after surgery. All patients received local radiation to the prostate and seminal vesicle bed. The primary outcome measured was distant metastasis after SRT. Regression tree analysis was used to develop a risk-stratification tool. Multivariable Cox regression analysis and non-parametric curve fitting methods were used to explore the relationship between PSA level at SRT and the probability of metastasis-free survival at 8-yr.
Results. At a median follow-up of 8.0 years, 130 patients (14%) developed distant metastasis. At multivariable analysis, pre-SRT PSA level was significantly associated with distant metastasis [HR: 1.01; p<0.0001]. However, when patients were stratified into five risk groups using regression tree analysis (AUC: 85%), early SRT administration provided better metastasis-free survival in three groups only: low-risk– undetectable PSA after RP, Gleason score ≤7, and tumor stage ≥pT3b; intermediate-risk– undetectable PSA after RP with Gleason score ≥8; high-risk– PSA persistence after RP with Gleason score ≤7.
Conclusions. We developed an accurate risk stratification tool to facilitate the individualized recommendation for early SRT based on prostate cancer characteristics. Early SRT proved to be beneficial only in selected groups of patients who are more likely to be affected by clinically significant but not yet systemic recurrence at the time of salvage treatment administration.