ESTRO 2021 Abstract Book

S751

ESTRO 2021

Urology, Valencia, Spain; 8 Hospital Central de la Defensa Gómez Ulla, Radiation Oncology, Madrid, Spain; 9 Centro Nacional de Investigaciones Oncológicas, Prostate Cancer Unit, Madrid, Spain; 10 Hospital Universitario La Princesa, Medical Oncology, Madrid, Spain; 11 Hospital Universitario Ramón y Cajal, Medical Oncology, Madrid, Spain; 12 Hospital Universitario La Paz, Radiation Oncology, Madrid, Spain; 13 Hospital Universitario Sant Joan Reus, Radiation Oncology, Reus, Spain; 14 Hospital Universitario Ramón y Cajal, Urology, Madrid, Spain; 15 Hospital Provincial de Castellón, Radiation Oncology, Castellón, Spain; 16 Hospital Clínico Universitario de Valencia, Radiation Oncology, Valencia, Spain; 17 Instituto de Investigación Biomédica de Málaga, Medical Oncology, Málaga, Spain Purpose or Objective Changes in the PSA are widely used as biomarker for the monitoring of treatment outcomes on metastatic castration-resistant prostate cancer (mCRPC) in the clinical real-world setting. The early identification of mCRPC patients (pts) not benefitting from Abiraterone/Enzalutamide (Abi/Enz) could be of paramount importance for optimal treatment delivery and cost effectiveness. We aimed to evaluate clinical relevance of early PSA increase in mCRPC patients treated with next-generation hormonal treatments. Materials and Methods We retrospectively evaluated Abi/Enz-treated mCRPC pts from 11 hospitals between 2011-2020. Early PSA Progression (PSAProg) was defined as a 25% increase in PSA from baseline at 4 (PSAProg4) or 8 (PSAProg8) weeks after treatment initiation. PSA progression at 12 weeks (PSAProg12) was confirmed by a second reading. Uni- and multivariable (MV) Cox regression models were conducted to explore the association of PSAProg and overall (OS) and radiographic progression-free (rPFS) survival. Sensitivity (Se), specificity (Sp) and predictive values (PPV, NPV) for the association of early PSAProg with PSAProg12 were calculated. Results We analyzed 640 mCRPC pts; median follow-up: 30.2 months. 98 (15.3%); 124 (19.4%) and 125 (19.5%) pts had PSAprog at 4, 8 and 12 wks. PSAProg4 and PSAProg8 were significantly associated with confirmed PSAProg12. 51% of pts with PSAProg4 and 60.5% of pts with PSAProg8 had a confirmed PSAProg12. Only 8.1% of pts with no PSA prog at 4 wks and 3.8% of pts with no PSAProg8 had a confirmed PSAProg12. PSAProg4 had Se: 54%, Sp: 91%, PPV: 54%, NPV: 91% for the detection of PSAProg12. PSAProg8 had Se: 81%, Sp: 91%, PPV: 63%, NPV: 96% for the detection of PSAProg12. PSAprog at 4, 8 and 12 wks was significantly associated with OS and rPFS in uni- and MV Cox models (Table). Conclusion Early PSAProg in mCRPC pts treated with Abi/Enz is associated with shorter OS and rPFS and may help identify pts not benefitting from Abi/Enz before clinical or radiographic progression. Prospective validation studies are needed. PD-0909 Outcomes of metastasis-directed treatment of bone oligometastatic disease in prostate cancer P. Rogowski 1 , N. Schmidt-Hegemann 1 , C. Trapp 1 , R. Shi 1 , R. von Bestenbostel 1 , J. Ma 1 , C. Belka 1 , M. Li 1 1 University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany Purpose or Objective Compared with nodal oligometastatic disease, data describing outcomes of bone oligometastatic disease are sparse. The aim of this study was to evaluate the outcomes of metastasis-directed treatment (MDT) of up to 4 bone metastases in prostate cancer patients. Materials and Methods Clinical data of 80 consecutive oligometastatic patients with 115 bony lesions receiving MDT between 2011 and 2019 were retrospectively evaluated. Hormone-sensitive (77.5%) and castrate-resistant (22.5%) patients were included. MDT was delivered with conventional fractionated or stereotactic body radiotherapy (SBRT) techniques. Kaplan–Meier method, log rank test, as well as Cox regression were used to calculate biochemical and clinical progression free survival (bPFS / cPFS). Results At the time of MDT 31% of patients had de-novo synchronous oligometastatic disease, 46% had de-novo metachronous oligorecurrence after primary treatment and 23% had either de-novo oligoprogressive disease, repeat oligometastatic disease or induced oligometastatic disease. The median BED 3 was 93,3 Gy (range 75,8 Gy - 95,3 Gy). Concomitant ADT was administered in 69%. After a median follow-up of 23 months the median bPFS and cPFS were 16.5 and 21.5 months, respectively. The 2-year local control rate was 98.3%. In multivariate analysis, age ≤ 70 and concomitant ADT significantly correlated with treatment response. Nineteen patients with relapse (42.2%) had repeat oligometastatic disease. Fourteen patients with progression (31%) underwent a second course of MDT. No patients experienced grade ≥ 3 toxicities.