SAT-507 Silent Signals: A Case of Pheochromocytoma With Negative Dotatate Uptake

Abstract Disclosure: P. Sztachelski: None. A. Attre: None. A. Arigala: None. B. Esayag-Tendler: None. Background: Pheochromocytomas are neuroendocrine tumors arising from the adrenal medulla that secrete catecholamines. It is diagnosed by biochemical evaluation showing increased urine or serum metanephrines and CT or MRI followed by functional imaging. We present a case of pheochromocytoma that presented with elevated metanephrines but negative uptake on a Cu-64 Dotatate scan. Clinical CaseA 47-year-old man with well controlled hypertension on amlodipine was found to have an adrenal mass on CT during evaluation of abdominal pain. MRI redemonstrated a 6.9 cm right adrenal mass that did not show arterial enhancement or intrinsic fat signal. Biochemical evaluation showed elevated metanephrines at 16.00 nmol/L (n < 0.49 nmol/L), normetanephrines at 6.05 nmol/L (n <0.89 nmol/L), renin of 0.4 ng/mL/hr, DHEA-S of 70 ug/dL, aldosterone of 4 ng/dL, cortisol at 8.8 ug/dL, and an ACTH of 61.8 pg/mL (n < 63.3 pg/mL). Calcitonin was 3.3 pg/mL (n < 7.5 pg/mL). Cu-64 dotatate scan revealed a 6.7 cm right adrenal mass demonstrating no discernable radiotracer uptake. He received pre-operative prazosin and metyrosine, which were started after completion of the dotatate scan. Patient underwent an uncomplicated right adrenalectomy. Surgical pathology confirmed a 7.8 cm pheochromocytoma, with immunostaining positive for synaptophysin, chromogranin, and GATA3; testing was negative for CKAE1/AE3 and Melan-A. Up to 1 mitosis/ 10 hpf was identified. Immunostaining with antibody Ki67 (MIB 1) stained < 1% of neoplastic cells. Normal immunohistochemical staining for succinate dehydrogenase B was noted. Genetic testing did not detect hereditary paraganglioma/ pheochromocytoma. Plasma metanephrines measured post-operatively showed metanephrines of < 0.10 and normetanephrines of 0.30. Conclusion: We report a case of pheochromocytoma with positive biochemical testing but negative uptake on a Cu-64 dotatate scan. Cu-64 dotatate PET/CT has sensitivity of 90-95% and specificity of 85-95% in detecting neuroendocrine tumors and relies on somatostatin receptor-2 (SSTR-2) expression. False-negative dotatate scans have previously been reported in cases with small tumor size (<28 mm), poorly differentiated tumors, those with low levels of SSTR-2 expression, or high uptake by healthy adrenal glands. This case underscores the significance of evaluating patients with suspected pheochromocytomas through a comprehensive lens, incorporating all clinical, biochemical, and radiologic information—even when discordant—to ensure an accurate diagnosis and appropriate treatment. Presentation: Saturday, July 12, 2025