SAT-498 Diabetes Improvement After Asymptomatic Large Pheochromocytoma Surgical Intervention in a Patient with Colon Cancer: A Case Report

Abstract Disclosure: O. Lavrynenko: None. A. DeMarsilis: None. C. Jiang: None. M.K. Konopka: None. A. Gavrila-Filip: None. P. Sinha: None. K. Chen: None. Background: Pheochromocytomas are rare catecholamine-secreting tumors arising from the adrenal medulla, often presenting with hypertension and sometimes are associated with diabetes. While they frequently present with symptoms, such as palpitations and sweating, pheochromocytomas can also manifest no symptoms and are discovered incidentally during imaging studies for unrelated conditions. The prevalence of asymptomatic or "silent" pheochromocytomas has increased due to advancements in imaging modalities, such as CT and MRI, which frequently detect adrenal masses during evaluations for other diseases. Case Presentation: A 73-year-old man with a history of hypertension and type 2 diabetes mellitus (diagnosed 3 years ago) presented with abdominal pain. Imaging revealed a suspicious colon mass suspicious for malignancy, along with a 7 cm right adrenal mass. He was admitted for surgical evaluation, and an endocrine consultation was obtained for preoperative hormonal assessment of the adrenal mass. Imaging confirmed a 7.1 × 6.7 × 6.7 cm adrenal mass, raising concern for pheochromocytoma, adrenal cortical carcinoma, or metastatic disease. During hospitalization, he experienced persistent hyperglycemia (blood glucose levels of 200-300 mg/dL), requiring basal-bolus insulin therapy.Initial hormonal evaluation revealed elevated normetanephrine and total free metanephrines. Urinary metanephrine and catecholamine levels were within normal limits, except for a slight elevation on one test. The patient was started on doxazosin for possible pheochromocytoma. The patient underwent a low anterior resection of the colon cancer, right adrenalectomy, and colorectal anastomosis. Postoperatively, the patient remained hemodynamically stable without signs of adrenal insufficiency and was discharged in good condition. Pathology confirmed the right adrenal mass was a benign pheochromocytoma. Following surgery, the patient felt well, and his blood pressure was well-controlled on lisinopril alone. Importantly, his diabetes improved significantly. He stopped insulin and did not resume glipizide and maintain good control of diabetes on metformin alone (blood glucose consistently less 200 mg/dl). He has since initiated chemotherapy for colon cancer. Conclusion: This case highlights the incidental discovery and asymptomatic nature of a large pheochromocytoma in a patient undergoing evaluation for another malignancy. The removal of the pheochromocytoma led to improved glycemic control, demonstrating the role of catecholamine excess in exacerbating diabetes. Presentation: Saturday, July 12, 2025