Introduction: Neuroendocrine tumors (NETs) are rare neoplasms arising neurologic or endocrine tissues. These tumors can be seen in nearly any organ system, though they mostly would be present in the gastrointestinal and respiratory systems. In this study, we report two cases of multi-visceral transplantations (MVT) in NET and discuss our indications for MVT among NET patients.

Methods and Results: Case 1: A 44-year-old lady referred with a complaint of acute abdominal pain and small bowel obstruction symptoms in June 2018. In laparotomy, an obstructive jejunal mass, a huge retroperitoneal lesion involving the mesentery and liver, was found. A partial resection of the jejunal mass and palliative anastomosis of the bowel was performed. Histopathologic examinations revealed a well-differentiated NET [G1 (ki67:1%)]. The patient underwent MVT. She developed an entero-cutaneous fistula ten days after the surgery which was managed. After which the patient was relatively well till February 2021, when she was admitted with severe watery diarrhea. Severe mucosal ulcerations were seen in endoscopy, and rejection was confirmed through pathologic assessments. The patient died despite our efforts. 
Case 2: A 46-year-old man who had been suffering from vague abdominal pain and dyspepsia was referred to our clinic in February  2021. He gave a history of 5 kilograms weight loss in the preceding six months. Computed tomography (CT) showed a large lobulated heterogeneously enhancing mass about 150*90 mm in the pancreas with extension to the liver hilum and involvement of spleen and stomach, and signs of partial port vein thrombosis. The pathologist reported a well-differentiated NET (G2, ki67<15%, mitosis 1-2/10 HPF). Exploratory laparotomy, performed in May 2021, showed locally advanced pancreatic NET with celiac encasement and involvement of stomach and colon and portal vein thrombosis with varicose veins and portal hypertension, but no evidence of hepatic metastases.
MVT was performed in June 2021. The grafts, including stomach, duodenum, liver, pancreas, and small bowel, were implanted. One month later, the patient complained of diarrhea, 3rd-grade acute T-cell rejection, in a small bowl biopsy was reported. However, the liver biopsy was insignificant. Favorably the patient responded well to the treatment, and after six months, closure of ostomy was performed. The patient is alive and well to this day.

Conclusion: We propose the following criteria for MVTx in NETs: Well-differentiated NETs; absence of progression in the last six months; extensive porto-mesenteric thrombosis; intestinal failure with liver metastases; Both superior mesenteric artery and celiac trunk involvement; absence of extra-abdominal involvement that is confirmed by Ga-68 dotatate scan. We should note that this was a case report and larger series are required to support our conclusion.