ESTRO 2025 - Abstract Book

S2047

Clinical - Urology

ESTRO 2025

Purpose/Objective: The PART Trial investigates the potential benefits of elective para-aortic radiotherapy (PART) added to whole pelvic radiotherapy (WPRT) and 24 months of androgen deprivation therapy (ADT) in patients with pN1 prostate cancer. The trial protocol was published in 2018 (1). Material/Methods: This multicentric, non-randomized phase 2 trial enrolled 138 prostate cancer patients between February 2017 and August 2024 with at least 2 pathological lymph nodes and/or extracapsular extension after extended pelvic lymph node dissection (EC2017/S59533). Patients received adjuvant or salvage radiotherapy to the prostate/prostatic fossa to respectively 65Gy/2.6Gy or 70Gy/2Gy and the pelvic and para-aortic lymph nodes to 45GY/1.8Gy, concomitant with long-term ADT. The primary endpoint is 5-year clinical recurrence-free survival (cRFS). Secondary endpoints include 5-year biochemical recurrence-free survival (bRFS), time to palliative ADT (pADT), prostate cancer-specific survival (PCSS), and treatment-related toxicity. Results: Oncological outcomes were analyzed for the initial 96 patients treated in the PART trial: 63 in the adjuvant setting and 33 in the early salvage setting. All patients were at least 12 months free of ADT, with testosterone levels still at castration levels in only 4%. At a median follow-up of 50 months (IQR 30-63), the 5-year cRFS rate was 81% (95% CI: 71-90), with significantly better cRFS in patients receiving adjuvant radiotherapy compared to salvage radiotherapy (92% vs 76%; p = 0.029) (See figure 1). The 5-year bRFS was 76% (95% CI 66-87), with the median bRFS not yet reached. A significant difference in bRFS was observed between the adjuvant and salvage group (90% vs 64%; p = 0.0006).

The cumulative incidence of acute grade 2 genitourinary (GU) and gastrointestinal (GI) toxicity was 49% and 51%, respectively. Acute grade 3 GU and GI toxicities occurred in 1.5% and 0.5% of patients, respectively. Late grade 3 GU toxicity was observed in 8% of patients, with no reported cases of late grade 3 GI toxicity (See figure 2). In-field control was achieved in 97% of patients. All clinical recurrences were classified as oligorecurrent disease (max 5 metastases). At the last follow-up, only six patients had initiated pADT, with one progressing to castration-resistant prostate cancer (CRPC) 24 months after starting pADT. The 5-years PCSS rate was 99%.