Serotonin-producing neuroendocrine tumors of the small intestine (SI-NETs; or mid-gut carcinoids) are well-differentiated, slow-growing tumors. Although SI-NETs are relatively uncommon, they represent the most frequent tumor of the distal small intestine.1–5 Clinical diagnosis of SI-NET is difficult owing to their slow tumor growth and mild symptoms, and many patients with SI-NET are often diagnosed late with advanced disease and a poor prognosis.1–5 Earlier studies proposed that these tumors were derived from intraepithelial enteroendocrine cells (EECs).