Candidates to salvage therapy after external-beam radiotherapy of prostate cancer: Predictors of local recurrence volume and metastasis-free survival.

PURPOSE: The purpose of this study was to assess the predictors of metastasis-free survival (MFS) and of the volume of the local recurrence in patients with rising prostate-specific antigen (PSA) serum level after radiotherapy for prostate cancer and referred for prostate magnetic resonance imaging (MRI) and biopsy in view of salvage treatment. MATERIALS AND METHODS: A total of 132 consecutive men (median age, 70 years; IQR, 66-77 years) with rising PSA after prostate radiotherapy who underwent prostate MRI and biopsy in view of salvage treatment between January 2010 and July 2017 were retrospectively evaluated at a single center. MFS predictors were assessed with Cox models. Predictors of the volume of the local recurrence (number of invaded prostate sectors at biopsy) were assessed using Poisson regression among variables available at PSA relapse. RESULTS: At multivariate analysis, an initial Gleason score≥8 (OR=7 [95% confidence interval (CI): 1.2-40]; P=0.03), a recent radiotherapy (OR=17 [95% CI: 3.9-72]; P<0.0001), the use of androgen deprivation therapy at PSA relapse (OR=12.5 [95% CI: 2.8-57]; P=0.001) and the number of invaded prostate sectors (OR=1.5 [95% CI: 1.1-2]; P=0.007) and maximum cancer core length (OR=0.7 [95%CI: 0.6-0.9]; P=0.002) at biopsy performed at PSA relapse were significant MFS predictors. The PSA level at relapse was significant independent predictor of the volume of local recurrence only when used as a continuous variable (P=0.0002) but not when dichotomized using the nadir+2 threshold (P=0.41). CONCLUSION: Pathological and clinical factors can help predict MFS in patients with rising PSA after prostate radiotherapy and candidates to salvage treatment. The PSA level at relapse has strong influence on the local recurrence volume when used as a continuous variable.