MON-120 - A Rare Case of MEN1 Syndrome Phenotype: Giant Prolactinoma Associated with an Adrenal Oncocytic Adenoma.

Introduction
Multiple Endocrine Neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by parathyroid adenomas, pituitary tumors, and enteropancreatic tumors. Among pituitary tumors, prolactinomas are the most common and often present at a young age. Adrenal involvement in MEN1 varies widely (20%–73%), likely due to differences in imaging practices. Most adrenal lesions are benign nonfunctional adenomas; however, giant invasive macroprolactinomas and clinically significant large hormonally active adrenal neoplasms—particularly oncocytic adrenal tumors, which are rare—are uncommon, especially in young patients.
Clinical case
A 21-year-old male with long-standing obesity and chronic headaches since age 14 was diagnosed with poorly controlled diabetes mellitus in 2024. At the end of 2024, he developed progressive visual disturbance. Ophthalmologic evaluation revealed bitemporal visual field loss, prompting neuroimaging. MRI showed a 3.7-cm giant pituitary macroadenoma with suprasellar extension and optic chiasm compression. Labs showed prolactin 3293 ng/mL, undetectable FSH and LH, total testosterone 620 ng/dL, ACTH 29 pg/mL, cortisol 3 µg/dL, IGF-1 215 ng/mL, and A1c 11.8. In retrospect, he reported delayed puberty, mild galactorrhea since age 16, and short stature.
Due to worsening vision loss, he underwent transsphenoidal surgery in early 2025. Intraoperatively, a giant invasive macroadenoma was noted, extending into the sphenoid sinus and clivus, with partial preservation of normal pituitary tissue. Postoperatively, prolactin fell to 40 ng/mL, and cabergoline was started. He was found to have secondary adrenal insufficiency (POD2 cortisol 3 µg/dL with low ACTH) and was started on hydrocortisone.
Follow-up showed persistently suppressed gonadotropins with high testosterone (821 ng/dL). DHEA-S was markedly elevated (>1800 µg/dL). Metanephrines and normetanephrine were normal. Cross-sectional imaging in mid-2025 revealed a 6.5-cm right adrenal mass (absolute washout 73%, relative washout 55%). FDG-PET showed avid uptake, raising concern for malignancy. He then underwent right adrenalectomy; pathology showed an oncocytic adrenocortical neoplasm. Given the pituitary macroadenoma and adrenal mass, genetic testing confirmed a pathogenic heterozygous MEN1 variant. Postoperatively, testosterone dropped to 62 ng/dL and DHEA-S to 607 µg/dL; the most recent DHEA level is 68.
Conclusions
This case highlights a rare MEN1 presentation in a young adult, featuring a giant invasive macroprolactinoma with visual compromise and a rare functional adrenal oncocytic neoplasm. Early recognition of MEN1 is key in patients with aggressive pituitary tumors and atypical endocrine neoplasms, as timely multidisciplinary care can prevent irreversible complications and guide long-term surveillance.

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