A case of conversion surgery for a pancreatic neuroendocrine neoplasm with tumor seeding-related peritoneal dissemination after endoscopic ultrasound-guided fine-needle biopsy.

BACKGROUND: Peritoneal dissemination (PD) following endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) is rare, particularly in pancreatic neuroendocrine neoplasms (PanNEN). Clinical indications for conversion surgery (CS) in PanNEN patients with PD remain poorly defined. CASE: A 65-year-old man was referred for evaluation of a pancreatic tail mass detected during bladder cancer treatment. EUS-FNB diagnosed PanNEN (G2). Laparoscopic distal pancreatectomy (LDP) was aborted after multiple PD nodules were identified within the lesser sac. Peritoneal cytology was negative, and no PD-suspected nodules were identified outside the lesser sac, raising suspicion of FNB‑related tumor seeding. Because lanreotide therapy maintained stable disease for 18 months without the development of distant metastasis, CS was planned. LDP with regional lymphadenectomy was successfully performed, achieving R0 resection. Pathology showed a well-demarcated pancreatic tail tumor and a white nodule with identical immunohistochemical profiles, suggesting a common origin. No evidence of recurrence has been observed at 4 months postoperatively. CONCLUSION: Given the rarity of PD and FNB-related tumor seeding in PanNEN, the present case provides valuable clinical insight into both the potential procedural risk and the feasibility of multimodal management incorporating systemic therapy, followed by curative-intent CS. CS may be a feasible option for selected PanNEN patients with PD after EUS-FNB.