MON-379 The Great Masquerade: Hypercalcemia as the Initial Presenting Sign of Malignant Pheochromocytoma

Introduction: Non iPTH mediated hypercalcemia as the initial presentation for malignant pheochromocytoma is a rare finding. Clinical Case: A 49-year male with a history of hyperlipidemia, pleomorphic adenoma of the salivary gland at age 25, presented with new onset diffuse headache of six months duration. This was associated with elevated blood pressure on multiple occasions, diaphoresis, ten pound weight loss, palpitations and tachycardia. His family history was significant for lung cancer. Initial blood tests were significant for severe hypercalcemia, calcium 13mg/dl (8.6-10.3mg/dl). CT brain with/without contrast was normal. CT chest, abdomen and pelvis with contrast showed a 9.9x11.7cm neoplastic soft tissue adrenal mass with marked peripheral tumor vascularity. Further laboratory workup showed 25 hydroxy vitamin D 18 ng/ml (30-100 ng/ml), 1,25 Dihydroxy vitamin D 106 pg/ml (18-72 pg/ml), PTH 6 pg/ml (14-64 pg/ml), PTHrp 35 pg/ml (14-27 pg/ml), total metanephrines and normetanephrines 11, 345 pg/ml (<205 pg/ml), and total catecholamines 16,465 pg/ml (123-671 pg/ml). Morning cortisol, TSH, TB Gold test, uric acid, calcitonin, ACTH and LDH were normal. MRI abdomen confirmed the 9.1x10.8x13.6cm centrally necrotic hypervascular right adrenal soft tissue mass with no adenopathy. PET scan revealed similar findings with standardized uptake values (SUV) Max 18.6 consistent with malignancy and C6 vertebral body tracer avid osteolytic lesion with SUV max 15 consistent with metastasis, that was confirmed on a MRI cervical spine as a 1.4 cm lesion. Further workup including MIBG scan revealed a C6 spine lesion suggestive of metastatic pheochromocytoma. He was diagnosed with malignant pheochromocytoma based on his symptoms, findings of the right adrenal mass on imaging, elevated serum norepinephrine, chromogranin A and urine total metanephrine and catecholamines. He received zoledronic acid 4mg IV resulting in normocalcemia. Subsequently, he underwent embolization of right adrenal vasculature followed by right radical adrenalectomy. Pathology confirmed pheochromocytoma with no vascular or capsular invasion with focal necrosis, pleomorphic cell features with high cellularity suggestive of potentially more aggressive behavior. The tumor was stained for PTH which was negative. Postoperatively, PTHrp decreased to <10pg/ml without any intervention to the metastatic osteolyic lesion. Genetic testing showed variant of uncertain significance. Conclusion: We report a rare case of humoral hypercalcemia of malignancy secondary to a malignant pheochromocytoma with PTHrp production.