Experience of 25 Patients Treated with Echoendoscopically Implanted 32 P Microparticles Associated with Chemotherapy in Locally Advanced Pancreatic Adenocarcinoma.

e16455 Background: Phosphorous 32 microparticle ( 32 P) brachytherapy delivered by echoendoscopy (EUS) represents an innovative therapy in pancreatic cancer (PC). Our aim is to evaluate efficacy and safety outcomes for Spanish patients in real clinical practice. Methods: After being assessed by a multidisciplinary committee and meeting eligibility criteria (Table 1), patients signed consent to receive intratumoural 32 P by EUS within the international observational registry OSPREY (March 2022-January 2025). Complications associated with intratumoural 32P injection via EUS, associated adverse events (AEs) and preliminary efficacy results (progression-free survival [PFS] and overall survival [OS]) were analysed. Results: Twenty-five patients (16 females and 9 males; age 67 years [range 48, 80]; 20 ECOG 1 and 5 ECOG 0) with unresectable locally advanced PC (16 in head, 4 in uncinate and 5 in body; tumour size 31.5 mm [range 12, 60]) were included. Seven patients (28%) had received a previous treatment. 23 patients (92%) received gemcitabine-based chemotherapy concomitant with intratumoural 32P (17 gemcitabine plus nabpaclitaxel; 6 gemcitabine monotherapy), 1 patient FOLFIRINOX and 1 patient did not receive concomitant chemotherapy. Two patients had AEs related to 32P injection by EUS: G2 asthenia and G1 abdominal pain, respectively. Seventeen patients (68%) had chemotherapy-related AEs, with 3 cases of G3 neutropenia and 1 of G3 thombopenia; 14 had G1-2 toxicities: neutropenia (3), thrombopenia (4), neurotoxicity (4), anaemia (2), asthenia (3), hyporexia (1), nausea (1), diarrhea (1) and constipation (1) . Four (16%) patients underwent surgery after intratumoural treatment. With a median follow-up of 17.2 months after injection, 14 patients (56%) have progressed, 13 distantly and 7 also locoregionally; 1 patient progressed only locally. The median PFS since 32P injection is 8.4 months (95% CI 4.3, 17.0). 12 patients are alive at the end of follow-up (48%) with a median OS since 32P injection of 13.8 months (95% CI 9.4, 26,9]. Conclusions: The experience of Spanish centres suggests that intratumoural 32P associated with gemcitabine-based chemotherapy is safe and achieve long survival. Our ongoing prospective registry will allow evaluation of the oncological outcomes of this therapy at longer follow-up times. Eligibility criteria. Inclusion criteria Exclusion criteria - Patients eligible for and undergo 32P implantation at an eligible treatment facility according to the approved instructions for use, as part of their clinical care. - Patients participating in an interventional clinical study. - Patients who have completed and signed the patient informed consent form (PICF) for the OSPREY Patient Registry. - Patients using an investigational agent at the time of enrolment.