SUN-096 - Dopamine Agonist-Resistant Giant Prolactinoma Requiring Multidisciplinary Management: A Case Report

Background: Giant prolactinomas are rare pituitary tumors that may demonstrate dopamine agonist resistance, posing significant management challenges. They are frequently complicated by vision loss, hypopituitarism, and residual disease, often requiring multidisciplinary care.

Case description: A 27-year-old man presented in Ghana in January 2023 with progressive vision loss. Workup revealed a 5.1 x 2.6 x 2.9 cm pituitary mass, prolactin (PRL) 8,987 μg/L, and bitemporal hemianopsia, consistent with giant prolactinoma. He had hypogonadotropic hypogonadism and central hypothyroidism, with no other pituitary dysfunction. Cabergoline and levothyroxine (LT4) were started; however, despite cabergoline dose escalation, his visual deficits worsened. He underwent transsphenoidal debulking in Ghana in October 2023, resulting in PRL reduction to 123 μg/L on cabergoline and partial visual improvement in his right eye. He relocated to the U.S. in August 2024 and presented with recurrent hyperprolactinemia (PRL 2,250 ug/mL) after stopping cabergoline, which was subsequently restarted. He established care in our Pituitary Multidisciplinary Clinic in November 2024, with PRL 1,655 μg/mL on cabergoline 0.5 mg twice weekly, TSH 2.4 mIU/L and fT4 1.2 ng/dL on LT4 100 μg daily, and PM testosterone 97 μg/dL. MRI showed substantial residual tumor with clival extension and bilateral cavernous sinus involvement. Cabergoline and levothyroxine were further up-titrated, and he was evaluated by neurosurgery and neuro-ophthalmology. Visual field exam demonstrated persistent bitemporal hemianopsia, worse in the left eye with a left afferent pupillary defect, suggesting permanent visual loss. MRI in February 2025 raised concern for slight tumor progression, prompting referral to radiation oncology and neuro-oncology for consideration of radiation and temozolomide; these interventions were deferred in favor of close imaging surveillance. MRI in July 2025 was stable, and his visual deficits were unchanged. He is currently on cabergoline 2 mg twice weekly, LT4 125 μg daily, and testosterone therapy for persistent hypogonadism (~150 μg/L) despite improved PRL control. Most recent laboratory testing showed PRL 66 μg/L, TSH 1.1 mIU/L, fT4 1.2 ng/dL, and testosterone 498 μg/L.

Conclusion: Giant prolactinomas with dopamine agonist resistance represent a distinct clinical entity that often deviates from the typical clinical course of most prolactinomas. This case highlights the challenges encountered in managing these tumors, including the need for high doses of cabergoline, surgical debulking for vision preservation, and persistent hypopituitarism. It also underscores the importance of multidisciplinary collaboration and coordinated care across multiple subspecialties. Long-term surveillance and comprehensive endocrine management remains essential for optimizing patient outcomes.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*