SAT-474 Giant Prolactinoma Case Series Assessing Response on Initial Dose of Cabergoline

Background: Giant prolactinomas (GPs) are rare representing 2-3% of prolactinomas and only ~ 0.5% of all pituitary tumors. Various definitions have been proposed for GP but commonly accepted criteria is tumor dimension of ≥4 cm. GP is often associated with very high prolactin (PRL) ranging 1,000 -100,000 ng/ml, significant extrasellar extension and no concomitant growth hormone or ACTH secretion. Patients predominantly present with neurological symptoms rather than endocrine dysfunction, and so the primary goal of treatment is amelioration of neurological symptoms. The literature search reveals approximately 190 papers on this topic and most are single case reports or series describing only unusual clinical manifestations. Hence, evidence based recommendations for treatment are lacking. Dopamine agonist (DA) is considered first line of therapy, as these tumors are highly sensitive to medical therapy. Surgery and radiation may be warranted in special situations. Low starting doses of cabergoline (CAB) are generally recommended due to concern for complications of apoplexy and cerebrospinal fluid (CSF) leak from rapid tumor shrinkage. However, no recommendations for a specific starting dose exist. Objective: Individual tumor and hormonal response were assessed on 15 patients (pts) with GP on low dose CAB; 0.25-0.5 mg weekly to determine the effectiveness of DA therapy. Methods: 15 GP pts from two tertiary care centers, meeting the diagnostic criteria mentioned above, were reviewed. Reduction in tumor volume and maximal tumor diameter along with PRL, after initiation of CAB, at or before 6 months and 1 year post diagnosis, was calculated. Results: Presenting symptom: visual disturbance (56%), headache (20%), apoplexy (13%) and incidental finding (6%). Mean age at diagnosis: 61 years. Male to Female: 4: 1. Basal prolactin concentration: >2000 ng/dl (12/15pts), and > 900 ng/ml (2/15). Initial total CAB dose/week: 0.25-0.5 mg (13/15) and 1-2 mg (2/15). Cranial surgery: 4/15. Complications: CSF leak (1/15). Tumor volume assessed at 6 months (11/15) and 1 year (4/15) along with decrease in maximum tumor diameter in the same period of time. PRL assessed at or before 6 months (13/15) and at 1 year (2/15). Improvement in tumor size occurred promptly even with low dose CAB (0.25-0.5mg/week). 100% of patients initiated on low dose CAB responded to therapy. Mean reduction in tumor volume at or before 6 months was 47% in 11/15, and 52% at 1 year (10/15). Mean decrease in maximal tumor dimension was calculated as 0.95 cm at 6 months (12/15) and 1.4 cm at 1 year (9/15). The overall prolactin response rate at or before 6 months was > 90% in 7/15 patients (53%) and >50% in 11/15 patients (73%). Conclusion: Our data confirms excellent tumor response to low dose cabergoline therapy. Dose as low at 0.25 mg twice weekly is proven to be effective, leading to decrease in both tumor volume and PRL levels.