J Naidu1,2,5, N Singhal.4, CH Yong4, J Zobel1, A Lim1,2, W Hsieh3, B Crouch3, K Ho3, D Calnan3, D Bartholomeusz1,2,3 and NQ Nguyen1,2

1Department of Gastroenterology and Hepatology, Royal Adelaide Hospital, Australia, 2School of Health and Medical Sciences, University of Adelaide, Australia, 3Department of Nuclear Medicine, Royal Adelaide Hospital, 4Department of Medical Oncology, Royal Adelaide Hospital, 5Department of Gastroenterology, National University of Malaysia Medical Centre, Kuala Lumpur, Malaysia

Background/Aims: Up to 80% of patients with pancreatic ductal adenocarcinoma (PDAC) present with locally advanced or metastatic disease. Our initial study (Naidu et al. Endoscopy 2021) indicated that chemotherapy and endoscopic ultrasound (EUS) guided intra-tumour 32P (OncoSil™) implantation was associated with tumour size reduction and down-staging of locally advanced pancreatic cancer (LAPC), resulting in successful R0 resection in 42% of patients. Its role in local disease control in patients with metastatic PDAC has not been defined. We sought to evaluate outcomes of combined chemotherapy and intra-tumoural 32P for metastatic PDAC.

Methods: Consecutive patients with histologically proven LAPC with imaging evidence of metastatic disease in the liver or lung with ECOG performance status 0 and 1 underwent EUS-guided 32P implantation to the primary lesion for local disease control. All patients received concurrent adjuvant chemotherapy with either FOLFIRINOX, gemcitabine/abraxane or targeted therapy as clinically indicated, with a minimum of 3-monthly clinical follow-up.

Results: A total of six patients (4 F, median age 64, 52-73 years) underwent combined therapy with 32P implantation at 3 to 8 months after diagnosis (median 5 months). All EUS guided implantations were technically successful with a mean injected volume of 2.5ml (17.8MBq) of 32P OncoSilTM. The implantation was well tolerated in all subjects with Bremsstrahlung scans confirming localisation of 32P 4 hours post-procedure. Chemotherapy was given for a median duration of 12.5 months (2-25 months). After a median follow-up of 21 months (11-26 months), 3 (50%) patients remain alive, and the median survival was 13 months (11-25 months) from diagnosis. At 20 weeks after implantation, there was no increase in tumour diameter (median 31.5mm vs 28.5mm; p=0.95), demonstrating excellent local disease control.

Conclusion: In metastatic PDAC EUS-guided 32P implantation appears to be safe with good local disease control and survival. These promising findings warrant further evaluation in a larger trial.

Keywords: Endoscopic Ultrasound, Pancreatic Cancer, Metastatic, Brachytherapy, Intratumoral injection