: Neuroendocrine tumors (NETs) of duodenal origin are an unusual subset among all NETs, comprising only about 3% of this neoplasm class. In general, NETs are characterized by overexpression of somatostatin receptors and carry an excellent prognosis with early diagnosis and intervention. Chromogranin A (CgA), a protein originating in secretory vesicles of neurons and endocrine cells, has gained wide usage in NET diagnosis and surveillance. Lanreotide is a synthetic octapeptide somatostatin analog with potent anti-proliferative action which has been approved by the FDA (U.S.) and EMA (E.U.) for NET treatment. It is known for its inhibitory effects on growth hormone, serotonin, CgA, and other markers. Here we describe a 56yr-old female with functional NET of duodenal origin, where serum CgA was successfully reduced from 3636 to <100 ng/mL after multidose lanreotide within five months. Of note, no metastatic spread was identified on positron emission tomography/computed tomography with 64Cu-labeled somatostatin analog tracer. Surgical resection of distal antrum, pylorus, and proximal duodenum was completed without complication. Histology revealed well-differentiated tumor cells with characteristic neuroendocrine features and clear surgical margins; low proliferation index (2%) was noted on Ki-67 staining. While select laboratory and imaging modalities are available for diagnosis and monitoring of duodenal NET, this is the first reported therapeutic use of lanreotide in this NET setting. The observed serum chromogranin A attenuation, even before surgery, supports its effectiveness in management of primary nonmetastatic duodenal NET after resection.