Supplementary Material for: Grade 1 Hepatic Neuroendocrine Tumor with Peritoneal Metastases: Case Report -- Diagnostic Reasoning and Management Challenges

Introduction: Neuroendocrine tumors are rare neoplasms that commonly metastasize to the liver, while peritoneal metastases occur less frequently but are associated with poorer outcomes. This report presents a rare case of concurrent liver metastasis and peritoneal metastasis from a well-differentiated neuroendocrine tumor, emphasizing the diagnostic reasoning and multidisciplinary management involved. Case Presentation: A 62-year-old woman with a history of laparoscopic cholecystectomy was incidentally found to have multiple hypoechoic liver lesions and a mesenteric mass. Contrast-enhanced CT and MRI revealed hepatic and peritoneal nodules consistent with metastatic disease. Laparoscopic wedge resection of hepatic segments VI and VIII and biopsy of peritoneal implants confirmed a grade 1 neuroendocrine tumor positive for chromogranin A, synaptophysin, and INSM1, with a Ki-67 index of 2–3%. The patient underwent cytoreductive debulking surgery, achieving approximately 70% tumor reduction, followed by long-acting octreotide therapy. Postoperative recovery was uneventful, and follow-up imaging demonstrated no recurrence. Conclusion: This case report underscores the importance of early recognition and a multidisciplinary approach in managing indolent neuroendocrine tumors with multisite metastases. Combined surgical and medical strategies, including debulking surgery and octreotide therapy, can achieve durable disease control and favorable outcomes.