ESTRO 2025 - Abstract Book

S1982

Clinical - Urology

ESTRO 2025

2084

Digital Poster PSMA PET response vs PSA nadir with ADT & ARPI in oligometastatic hormone sensitive prostate cancer Parth Verma 1 , Prachi Adole 1 , Nimisha Sharma 1 , Prachi Mehta 1 , Archi Agarwal 2 , Suchismita Ghosh 2 , Sayak Choudhury 2 , Amit Joshi 3 , Venkatesh Rangarajan 2 , Priyamvada Maitre 1 , Vedang Murthy 1 1 Radiation Oncology, Tata Memorial Hospital, Mumbai, India. 2 Nuclear Medicine, Tata Memorial Hospital, Mumbai, India. 3 Medical Oncology, Tata Memorial Hospital, Mumbai, India Purpose/Objective: For patients with oligometastatic hormone sensitive prostate cancer (omHSPC), addition of androgen receptor pathway inhibitors (ARPIs) to androgen deprivation therapy (ADT) improves probability of achieving PSA nadir <0.1ng/ml in the first year of treatment. It is not known if the biochemical response is associated with to improved PSMA-based response which may guide further metastasis directed therapy (MDT). Material/Methods: Patients diagnosed with de-novo omHSPC (CHAARTED criteria) treated at a tertiary cancer care center were screened, with inclusion criteria - availability of PSMA-PETCT at primary diagnosis, treatment with ADT + ARPI for at least 3 months, PSMA-PETCT based response imaging at <12 months from starting treatment, followed by radiotherapy to prostate. For subgroups treated with ADT alone versus ADT + ARPI, biochemical response and PSMA PET-CT scans were compared from baseline and <12 months of systemic therapy. Response within the prostate, lymph nodes and bone metastases in the post-therapy PSMA-PETCT was evaluated using the PROMISE criteria v2.0, and compared between the two subgroups using chi square or Fisher’s exact test. Results: A total of 94 patients were eligible for analysis, of which 40 were staged M1a and 54 were M1b. ADT alone was received by 48 patients (51%) while 46 patients (49%) received ADT + ARPI (Abiraterone 41, Enzalutamide 5). Response assessment PSMA-PETCT was done at median 6 months (IQR 5-6.3 months) from initiation of systemic therapy. Nadir PSA <0.1ng/ml was achieved by 7/48 patients (14.6%) in ADT alone group versus 25/46 patients (54.3%) in ADT + ARPI group (p<0.0001). Metabolic responses in prostate, nodes, and bones, were noted in 82% vs 93%, 88% vs 92% and 69% vs 79% respectively, for ADT alone vs ADT + ARPI. (p=0.1, 0.7, 0.5). For patients reaching PSA <0.1 vs >0.1, metabolic response was similar in prostate (91% vs 86%), nodes (96% vs 87%) and bones (75% and 74%) (p=0.4, 0.4, 1.0). Conclusion: In this cohort, higher proportion of patients achieved PSA nadir <0.1ng/ml after treatment with ADT + ARPI vs with ADT alone. However, metabolic response was not different. Exploration of PSMA-PETCT-based response in a larger cohort may help optimize target site selection for MDT. References: 1. Sweeney CJ et al. Chemohormonal Therapy in Metastatic Hormone-Sensitive Prostate Cancer. N Engl J Med. 2015 Aug 20;373(8):737-46. 2. Matsubara N, et al. Correlation of Prostate-specific Antigen Kinetics with Overall Survival and Radiological Progression-free Survival in Metastatic Castration-sensitive Prostate Cancer Treated with Abiraterone Acetate plus Prednisone or Placebos Added to Androgen Deprivation Therapy: Post Hoc Analysis of Phase 3 LATITUDE Study. Eur Urol. 2020 Apr;77(4):494-500. Keywords: Metastatic Prostate, PSA response, ARPI