SUN-507 Bilateral Pheochromocytoma with Variant of Uncertain Significance in Rare MAX Gene

Abstract Disclosure: K.E. Fain: None. R. Ali: None. S. Raghunathan: None. Background: In 2011, the MAX (MYC-associated factor X) gene was first discovered to be responsible for hereditary pheochromocytoma; however, very few cases of bilateral pheochromocytoma due to MAX gene mutation have been reported. The MAX gene consists of 5 exons and is located on chromosome 14q23.3. This gene is a tumor suppressor responsible for regulation of cell proliferation, apoptosis, and differentiation. Interestingly, few case reports of bilateral pheochromocytoma secondary to MAX gene mutation have been documented in patients without family history or concurrent endocrinopathy. At this time, no specific clinical presentation has been associated with the MAX gene mutation due to low case numbers in the literature. Clinical Case: A 34-year-old female with no family history of endocrine neoplasia was admitted to the Medical Intensive Care Unit for hypertensive urgency and found to have a right sided adrenal mass measuring 9.2 x 9.6 x 7.6 cm, as well as two left adrenal nodules measuring 1.4 cm and 1.6 cm, respectively. Urine fractionated metanephrines revealed a value of 37,277 (36-229 ug/24 hours) and normetanephrine value of 28,404 (95-650 ug/24 hour). Plasma metanephrine was measured to be 22.20 (0-0.49 pmol/L), epinephrine was 4,715 (&lt 330 pmol/L), and norepinephrine was 23,283 (1050-4800 pmol/L). Given high likelihood of bilateral pheochromocytoma, the patient was initiated on Doxazosin for alpha blockade requiring up to 16mg twice daily. PET Scan showed intensely avid right adrenal mass and moderately avid left adrenal nodules confirming the diagnosis of bilateral pheochromocytoma. The patient underwent open right adrenalectomy and cortical sparing left adrenalectomy. She was initiated post operatively on a steroid taper for possible adrenal insufficiency. 24-hour metanephrine and normetanephrine levels normalized post-surgery. Genetic testing (Invitae) was positive for variant of uncertain significance (VUS) in the MAX gene with low risk for mutation. Conclusion: Few cases of bilateral pheochromocytoma secondary to MAX gene mutations have been documented in the literature; therefore, continued documentation and genetic testing is necessary. At this time, further research will be needed to assess clinical presentation, management strategies, association with syndromes, and effects due to MAX gene mutation. Presentation: Sunday, July 13, 2025