ABSTRACT
Pituitary tumors occur in 15-50% of patients with multiple endocrine neoplasia of type 1 (MEN1). To the best of our knowledge, no MEN1 case in which the initial lesion was an invasive giant prolactinoma has been reported from Korea. We describe a patient in whom a skull-base tumor involved the sellar and parasellar spaces. A 49 year-old female presented with headache and diplopia. The tumor was ultimately identified as a giant prolactinoma; the serum prolactin concentration increased from 155.6 ng/mL to 3,234.3 ng/mL after cranial irradiation. She was evaluated in terms of incidental hypercalcemia and was found to have parathyroid hyperplasia. Genetic analysis revealed a missense mutation in the MEN1 gene (c.643G>A, p.Val215Met). Two years of treatment with a dopamine agonist reduced, but did not normalize, the serum prolactin concentration. We highlight the aggressive behavior of the giant skull-base tumor, and the diagnostic delay caused by a high-dose hook effect of the MEN1-related prolactinoma.