Source of Funding: Janssen Research & Development MP24-09 BALANCING EFFICACY AND TOXICITY OF DOCETAXEL IN PATIENTS WITH METASTATIC CASTRATION-RESISTANT PROSTATE CANCER. RESULTS FROM A POOLED ANALYSIS OF THREE PROSPECTIVE RANDOMIZED TRIALS Alberto Martini, Giuseppe Cirulli*, Milan, Italy; Anish B. Parikh, John P. Sfakianos, Matthew D. Galsky, William K. Oh, Che-Kai Tsao, New York, NY; Giorgio Gandaglia, Nicola Fossati, Armando Stabile, Andrea Necchi, Vito Cucchiara, Francesco Pellegrino, Simone Scuderi, Milan, Italy; Pierre I. Karakiewicz, Montreal, Canada; Francesco Montorsi, Alberto Briganti, Milan, Italy INTRODUCTION AND OBJECTIVE: Docetaxel is widely used in metastatic castration-resistant prostate cancer (mCRPC), however its optimal use remains unclear. Biomarkers and prediction models assessing efficacy and toxicity of Docetaxel may help optimize treatment selection. METHODS: Through Project Data Sphere, we accessed patient data from the control arms of three frontline mCRPC trials: ASCENT2, VENICE, and MAINSAIL. Treatment in each control arm consisted of Docetaxel 75mg/m2 every 21 days þ prednisone 5mg twice/day. The primary outcome was occurrence of toxicity-related D discontinuation (TRDD). Reasons for Docetaxel discontinuation were recorded and extensive demographic and clinical data were considered in a competing risks regression (CRR) to develop a model to predict TRDD. Cumulative incidence (CI) of TRDD was estimated after accounting for the occurrence of competing events (death or progression). This model was used to build a risk calculator to predict TRDD, the output of which was used in a classification and regression tree (CART) to identify 3 risk groups. Overall survival (OS) for the pooled cohort and for each risk group was assessed via the Kaplan-Meier (KM) method. RESULTS: A total of 1568 pts were studied. Median follow-up was 12.1 mo. Median OS was 21 mos. CRR yielded the following significant factors that were included in the predictive model and risk calculator: age, ECOG performance status, AST, bilirubin, use of analgesics, and presence of diabetes and chronic kidney disease. Pooled CI of TRDD was 19% after accounting for competing events (death, 474 pts; progression, 59 pts) within 12 months of starting treatment. The CART analysis identified three risk groups: low (model-derived TRDD risk 24%), intermediate (25-64%), and high (65%) risk group. In each risk group, probability of TRDD during treatment was 14%, 58%, and 79%, and median OS was 24 months, 20 months, and 13 months, respectively (p<0.001). The KM survival curves for each group are shown in Fig. 1. CONCLUSIONS: For patients with mCRPC, our model can help clinicians balancing Docetaxel toxicity and efficacy. The three risk cat- egories identified correlated with OS and this is particularly useful for an optimal shared decision-making process. Source of Funding: MP24-10 NEWLY-DIAGNOSED LOW-VOLUME METASTATIC PROSTATE CANCER; IS THERE A PLACE FOR CYTOREDUCTIVE RADICAL PROSTATECTOMY? Elise De Bleser*, Nicolaas Lumen, Sarah Buelens, Wesley Verla, Wietse Claeys, Val erie Fonteyne, Sofie Verbeke, Geert Villeirs, Kathia De Man, Sylvie Rottey, Charles Van Praet, Karel Decaestecker, Piet Ost, Ghent, Belgium INTRODUCTION AND OBJECTIVE: Radiotherapy to the prostate (RTp) has recently been shown to prolong survival in patients with low-volume newly-diagnosed metastatic prostate cancer (ndmPC). Therefore it was suggested to be a possible standard of care treatment strategy in these patients. In contrast, to date, there is no data available whether cytoreductive radical prostatectomy (cRP) is equally beneficial as RTp for these patients. The objective was to evaluate the efficacy and safety of cRP in low-volume ndmPC. METHODS: Eligible patients had low-volume ndmPC and were included in this prospective, multicentric study. Patients were included from 2014 until the end of 2020. In total, 109 patients entered the study and were offered cRP, RTp or no local therapy (NLT) (48, 26, 35, respectively). Treatment allocation was dependent on patient's preference. Median follow-up was 32 months (IQR: 16-49). The aim was to compare the outcome of cRP to RTp and NLT. Kaplan-Meier statistics were used to assess overall survival (OS), cancer-specific survival (CSS) and local-event free survival (LEFS). Uni- and multivariate Cox regression analysis was used to identify prognostic factors influencing OS. RESULTS: 3y-OS was 87%, 100% and 69% and 3y-CSS was 87%, 100% and 75% for cRP, RTp and NLT, respectively. OS was better for cRP and RTp compared to NLT (p[0.007 and p[0.04, respectively). However, no difference in OS was observed between cRP and RTp (0.9) (Figure 1). The 3y-LEFS was 86%, 70% and 55% for cRP, RT and NLT, respectively. Following cRP, LEFS was better compared to RTp (p[0.02) and NLT (p[0.004). No significant differ- ence was seen between RTp and NLT (p[0.5). Negative prognostic factors for OS were advanced tumor stage, Eastern Cooperative Oncology Group 2 and NLT.Important selection bias was present as a consequence of treatment allocation being dependent on patient's preference. CONCLUSIONS: OS and CSS of cRP was similar to RTp and was better compared to NLT and is an effective treatment strategy to prevent local events. Vol. 206, No. 3S, Supplement, Saturday, September 11, 2021 THE JOURNAL OF UROLOGY Ò e415 Copyright © 2021 American Urological Association Education and Research, Inc. Unauthorized reproduction of this article is prohibited.