A Pituitary Macroadenoma Cosecreting Prolactin and Growth Hormone in a Patient With Multiple Endocrine Neoplasia Type 4

Multiple endocrine neoplasia type-4 (MEN4) is a rare form of multiple endocrine neoplasia due to a pathogenic variation in the cyclin-dependent kinase inhibitor 1B (<i>CDKN1B)</i> gene. It has a similar presentation to patients with multiple endocrine neoplasia type-1 (MEN1), with primary hyperparathyroidism and pituitary adenomas being the most common features. In this case, we describe a 54-year-old woman presenting with a pituitary macroadenoma cosecreting growth hormone and prolactin and primary hyperparathyroidism. She was initially managed with cabergoline without satisfactory response. Eventually she proceeded to transsphenoidal pituitary resection of the adenoma, and histology revealed appearances consistent with a mixed somatotroph-lactotroph adenoma. Subsequently genetic analysis confirmed the presence of a pathogenic variant in the <i>CDKN1B</i> gene (<i>CDKN1B c.410del</i>), in keeping with a diagnosis of MEN4. This is the first case of a cosecreting pituitary macroadenoma to be described in a patient with MEN4.