ESTRO 2025 - Abstract Book

S4417

Late-breaking abstracts

ESTRO 2025

4996

Proffered Paper PSMA PET/CT Stage Migration and Genomic Classifier Scores in High-Risk Prostate Cancer: First-Year Results from the THUNDER Trial (NCT06282588) Fleur Kleiburg 1,2 , Piet Dirix 3 , Valérie Fonteyne 4 , Samuel Bral 5 , Bart De Troyer 6 , Brieuc Sautois 7 , Maréva Lamande 8 , Nick Liefhooghe 9 , Guillaume Grisay 10 , Sabine Meersschout 11 , Ad Vandermeulen 12 , Nicolas Jullian 13 , Lorenzo Staelens 14 , Marla Johnson 15 , Eileen Kelly 15 , Filip Poelaert 16 , Michiel Strijbos 17 , Karolien Goffin 18 , Nadia Withofs 19 , Piet Ost 3 1 Department of Radiology, Section of Nuclear Medicine, Leiden University Medical Center, Leiden, Netherlands. 2 Biomedical Photonic Imaging Group, University of Twente, Enschede, Netherlands. 3 Department of Radiation Oncology, Iridium Network, Antwerp, Belgium. 4 Department of Radiation Oncology, Ghent University Hospital, Ghent, Belgium. 5 Department of Radiation Oncology, AZORG, Aalst, Belgium. 6 Department of Urology, VITAZ, Sint-Niklaas, Belgium. 7 Department of Medical Oncology, Centre Hospitalier Universitaire de Liège, Liège, Belgium. 8 Department of Radiation Oncology, Centre Hospitalier Universitaire de Liège, Liège, Belgium. 9 Department of Radiation Oncology, AZ Groeninge, Kortrijk, Belgium. 10 Department of Medical Oncology, Centres Hospitaliers Universitaires HELORA, La Louvière, Belgium. 11 Department of Radiation Oncology, AZ Sint-Jan, Bruges, Belgium. 12 Department of Radiation Oncology, Cliniques Universitaires Saint-Luc, Brussels, Belgium. 13 Department of Radiation Oncology, Institut Jules Bordet, Brussels, Belgium. 14 Department of Radiation Oncology, AZ Delta, Roeselare, Belgium. 15 Veracyte, Veracyte Inc, San Diego, USA. 16 Department of Urology, GZA Hospitals Sint-Augustinus, Antwerp, Belgium. 17 Department of Medical Oncology, GZA Hospitals Sint-Augustinus, Antwerp, Belgium. 18 Department of Nuclear Medicine, UZ Leuven, Leuven, Belgium. 19 Department of Nuclear Medicine and Oncological Imaging, Centre Hospitalier Universitaire de Liège, Liège, Belgium Purpose/Objective The ProPSMA trial showed that PSMA PET/CT upstaged 8% of high-risk prostate cancer to M1 disease [1]. Decipher prostate genomic classifier (GC) scores also have prognostic value, with 42% of patients with a score >0.85 developing distant metastases within 10 years [2]. The phase 2/3 THUNDER trial (NCT06282588) is investigating whether treatment adaptation based on PSMA PET/CT and GC scores improves metastasis-free survival in high-risk prostate cancer patients. This study analysed stage migration on PSMA PET/CT compared to conventional imaging, and the correlation between GC scores and PSMA PET/CT findings in patients screened in the first year of the trial. Material/Methods Patients with high-risk prostate cancer (at least one of the following criteria: PSA >20 ng/ml, T-stage 3-4, ISUP grade 4-5, and/or cN1 disease) referred for curative intent radiotherapy who gave informed consent between 13-12-2023 and 12-12-2024 were included. Patients with a screening failure due to M1 disease on conventional imaging were included in the analysis on stage migration (cohort 1: n=140), but excluded from the analysis on GC scores (cohort 2: n=133). Contrast-enhanced CT, 99m Tc-bone scintigraphy (planar + whole-body SPECT/CT) and PSMA PET/CT were performed within 16 weeks prior to screening, and assessed using the TNM classification, or the PROMISE V2 framework for PSMA PET/CT [3]. GC scores were provided by Veracyte (San Diego, USA). Results PSA >20 ng/ml was seen in 38% of patients, T-stage 3-4 in 61%, ISUP grade 4-5 in 73%, and cN1 disease in 19%. Compared to conventional imaging, PSMA PET/CT upstaged 42 patients (30%), with N1 upstaging in 23% and M1 upstaging in 13%. Upstaging risk increased with more high-risk features (Fig.1). Downstaging occurred in 1 patient (1%). In patients that met the STAMPEDE cM0 high-risk criteria (n=73)[4], PSMA PET/CT upstaged 37% of patients, with M1 upstaging in 19%. GC score was significantly associated with extraprostatic disease (Fig.2)(OR=1.29, 95% C.I.[1.05-1.58] per 0.1 increase, p=0.016), independent of PSA and ISUP grade.