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INTRODUCTION AND OBJECTIVES: Previous studies have shown that the efficacy of salvage radiotherapy (SRT) in men with biochemical recurrence (BCR) after radical prostatectomy (RP) is strongly related to PSA value at SRT. Contemporary guidelines suggest that SRT,when indicated, should be given at a PSA 0.5 ng/ml (early SRT eSRT). Such approach might be comparable in terms of cancer control to adjuvant RT while significantly reducing the number of patients exposed to RT. However, there is no available model for the prediction of BCR after eSRT. We developed and internally validated a model predicting BCR in patients treated with eSRT after RP for PCa METHODS: The study included 342 patients who received eSRT for BCR after RP at 6 European tertiary care centers between 1993 and 2006. Early SRT was defined as a salvage treatment given at a PSA 0.5 ng/ml. All patients had pT3, pN0, / positive surgical margins (SM). BCR after RP and eSRT was defined as two consecutive PSA values 0.2 ng/mL. No patient received adjuvant hormonal therapy. Radiotherapy consisted of a local radiation delivered to the prostate and seminal vesicle bed alone. Univariable (UVA) and multivariable (MVA) Cox regression models predicting BCR after eSRT were fitted. Predictors consisted of PSA at eSRT, time from RP to BCR, SM status, pT stage, radiotherapy dose and pathological Gleason score (6 vs. 7 vs. 8 or more). Regression-based coefficients were then used to develop a nomogram predicting BCR at 5 years after eSRT. The accuracy of the nomogram was quantified with the Harrel’s concordance index and the calibration plot method. Two hundred bootstrap resamples were used for internal validation. RESULTS: Mean follow-up was 81 months (median 68 months). Mean RT dose was 68 Gy (median 66.6 Gy,range:60-75.6 Gy). BCR-free survival rates at 2, 5 and 8 years after eSRT were 78.4, 61.5 and 56.8%, respectively. At univariable Cox regression analyses, pathological Gleason sum, PSA at eSRT and SM status were indipendent predictors of BCR after eSRT (all p 0.005). The results were confirmed at MVA where all mentioned predictors, including PSA at eSRT, were significantly associated with BCR after eSRT (all p 0.004). The coefficient-based nomogram demonstrated a bootstrapcorrected predictive accuracy of 74.7%. CONCLUSIONS: More than half of patients treated with eSRT for BCR after surgery had undetectable PSA at 5 years. We report the first nomogram predicting BCR in these patients. Our model might be used to assess the impact of eSRT according to each individual characteristics. Source of Funding: None