Early Local Tumour Control and Feasibility of Intratumoral P-32 Microparticle Implantation in Patients with Locally Advanced Pancreatic Cancer: A Prospective Single-Center Observational Cohort Study

Background: Evidence regarding EUS-guided intratumoral phosphorus-32 (P-32) microparticle implantation for locally advanced pancreatic cancer (LAPC) remains limited. This prospective pilot study evaluated its technical feasibility, preliminary safety, and early disease-control outcomes when administered in combination with gemcitabine plus nab-paclitaxel. Methods: Seventeen patients with unresectable LAPC underwent EUS-guided intratumoral P-32 microparticle implantation through a 22-gauge fine-needle aspiration needle during the fourth week of systemic chemotherapy. Intratumoral distribution was assessed using Bremsstrahlung SPECT/CT. Tumour response was evaluated according to RECIST version 1.1, and treatment-emergent adverse events were graded according to CTCAE version 4.0. The main secondary endpoint was local disease control rate at approximately 16 weeks (LDCR16w). All analyses were descriptive. Results: Implantation was technically successful in all 17 patients (100.0%; exact 95% CI, 80.5–100.0%), and SPECT/CT confirmed intratumoral distribution in every case. No implantation-related procedural complications were recorded (0/17; exact 95% CI, 0.0–19.5%). At approximately 16 weeks, CT assessment was available for 16 patients: seven had a partial response and nine had stable disease. The LDCR16w was 16/16 among evaluable patients (100.0%; exact 95% CI, 79.4–100.0%) and 16/17 in the all-treated analysis (94.1%; exact 95% CI, 71.3–99.9%). A reduction in CA19-9 of at least 50% was observed in 13/16 evaluable patients. Four patients underwent subsequent R0 resection (4/17, 23.5%; exact 95% CI, 6.8–49.9%). Adverse events were predominantly grade 1–2; one grade 3 abdominal pain event and no grade 4–5 events were recorded. Only three deaths occurred during a median OS follow-up of 15.6 months, making survival estimates exploratory and statistically immature. Conclusions: In this small, single-center pilot cohort of highly selected patients, EUS-guided intratumoral P-32 microparticle implantation combined with gemcitabine plus nab-paclitaxel was technically feasible and provided preliminary safety information. Because of the absence of a chemotherapy-only comparator, the small sample size, and the limited follow-up, the radiographic, biomarker, resection, and survival outcomes cannot be attributed specifically to P-32 implantation and should be considered descriptive and hypothesis-generating. Larger controlled studies with longer follow-up are required to determine clinical efficacy.