Context The selective arterial secretagogue injection test is a functional examination to determine localization of functional neuroendocrine tumor. Since the selective arterial secretagogue injection test capitalizes on the hormone-secreting ability of neuroendocrine tumor, no reports on this test in non-functional neuroendocrine tumors have yet been published. Objective In this study, we evaluate the utility of the selective arterial secretagogue injection test for non-functional neuroendocrine tumors. Methods The selective arterial secretagogue injection test was conducted in 8 non-functional neuroendocrine tumors cases. Results were compared to 10 functional neuroendocrine tumor (5 insulinoma, 5 gastrinoma) cases, and reactivity of insulin and gastrin was retrospectively considered. Insulin and gastrin immunostaining was conducted, and immunostaining results were compared with selective arterial secretagogue injection test reactivity. Results The insulin-positive rate following vasa vasorum stimulation was 75% (6/8), and that for distant vessels was 25% (2/8). Selective arterial secretagogue injection test reactivity and tumor localization were related. Insulin immunostaining was positive in 50% of cases (4/8). The increase in insulin in the selective arterial secretagogue injection test in negative immunostaining cases was 8.9 μU/mL, and that in positive immunostaining cases was 31.4 μU/mL. Positive immunostaining cases tended to have greater increases in insulin than negative immunostaining cases (P=0.089). Positive gastrin response rates were 75% (6/8), 100% (8/8), 0%, and 0% in the superior mesenteric artery, gastroduodenal artery, dorsal pancreatic artery, and proximal splenic artery, respectively. Gastrin immunostaining was negative in all cases, and no relationship between tumor localization and selective arterial secretagogue injection test reactivity was observed. Conclusion An increase in insulin response in non-functional neuroendocrine tumors suggests that tumors may have latent insulin secretory ability.
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