ESTRO 2025 - Abstract Book

S420

Clinical - Biomarkers

ESTRO 2025

3997

Poster Discussion PSA kinetics in predicting biochemical relapse in low and intermediate prostate cancer

Andrea G. Allegra 1 , Luca Nicosia 1 , Alessandro Molinari 2 , Nicola Bianchi 1 , Filippo R. Borghese 1 , Chiara De-Colle 1 , Antonio De Simone 1 , Christian Fierro 2 , Niccolò Giaj-Levra 1 , Francesca Giannetti 2 , Davide Gurrera 1 , Claudia Menichelli 2 , Stefania Naccarato 1 , Carolina Orsatti 1 , Gabriella Pastore 2 , Edoardo Pastorello 1 , Francesco Ricchetti 1 , Michele Rigo 1 , Andrea Romei 1 , Gianluisa Sicignano 1 , Paola Zuccoli 2 , Ruggero Ruggieri 1 , Alessandro Fanelli 1 , Filippo Alongi 1,3 1 Department of Advanced Radiation Oncology, IRCSS Sacro Cuore Don Calabria, Negrar, Italy. 2 Radiotherapy Department, Ecomedica Poliambulatorio Ergéa Group, Empoli, Italy. 3 Department of Radiation Oncology, University of Brescia, Brescia, Italy Purpose/Objective: Prostate cancer (PCa) remains one of the most prevalent malignancies in men, with radiation therapy (RT) as an important curative treatment for localized disease. Prostate-specific antigen (PSA) kinetics, particularly PSA reduction (PSAr) after RT, are emerging as significant prognostic indicators for long-term biochemical control. However, the correlation between PSAr and biochemical relapse-free survival (BRFS) remains underexplored. Material/Methods: This retrospective multi-institutional study analyzed 251 low- to intermediate-risk PCa patients treated with RT only between 2011 and 2020. Different RT schedules with similar isoeffective dose were included in the study. More specifically 39 fractions x 2 Gy, 28 x 2.55 Gy, 16 x 3.5 Gy, 5 x 7 Gy. Main objective of the study was BRFS, defined as the time from PSA nadir (PSAn) to a value of PSAn plus 2 ng/ml. PSAr was defined as the percentage of reduction of total PSA from baseline value. Cutoff Finder tool was used to determine the optimal PSAr cut-off, defined as the value with the most significant split (logrank test). The optimal PSAr cut-off value was defined as 90%. Patients were stratified by PSAr, baseline PSA, Gleason Score (GS), and RT schedules. Univariate analyses for survival endpoints were perfomed with the Kaplan-Meier method. The multivariate anlyses were performed by Cox proportional hazards model. Results: Median age was 75 years (range 45-85); GS was 6 in 120 (48%) patients and 7 in 131 (52%) patients; RT treatment included conventionally fractionated RT (55), hypofractionated schedules (127) and SBRT (69). After a median follow up of 36 months (range 30-48), 2 and 5-year BRFS were 97.3% and 95.2%, respectively, in patients with PSAr ≥90% and 89.5%, 61.5% in patients with PSAr<90% (p=0.00). In the responder population, median time to PSAr 90% was 24 months and the median time to PSA nadir was 28.7 months (range 20-38). At univariate analysis there were no significant BRFS differences for RT schedules (p=0.58), GS (p=0.2) and baseline PSA (p=0.053). Multivariate analysis confirmed PSAr as the only significant predictor of BRFS [HR 6.519 (95% IC 1.9-22.2), p=0.003]. Conclusion: Our findings suggest that PSAr could be a more reliable prognostic factor for long-term biochemical control than traditional markers. This study underscores the potential of PSAr as a clinical tool for risk stratification and personalized follow-up strategies in PCa management. Patients with suboptimal PSAr may benefit from intensified surveillance to mitigate relapse risk.

Keywords: PSA kinetics; Prostate Cancer; Biochemical Relapse