Prolactin-Secreting Lung Adenocarcinoma Metastatic to the Pituitary Mimicking a Prolactinoma: A Case Report

Background and importance Metastasis to the pituitary gland is uncommon in patients with systemic disseminated cancer. Individual articles have reported cases of pituitary metastasis mimicking a prolactinoma, but no case of a prolactin-secreting tumor metastasizing to the pituitary mimicking a prolactinoma has been reported so far. Clinical presentation This article reports a 67-yr-old man with a recent onset of headaches, ophthalmoplegia, hypopituitarism, and hyperprolactinemia who was initially diagnosed with prolactinoma and given bromocriptine in the local hospital. Because of vomiting after taking drugs, he was transferred to our hospital for further diagnosis and treatment. Serum prolactin was elevated up to 1022 ng/mL, and pituitary magnetic resonance imaging revealed a 2.9 × 2.8 × 2.3 cm sellar mass with pituitary apoplexy, for which endoscopic transsphenoidal surgery was performed. Postoperative pathology and western blotting disclosed a prolactin-positive metastatic lung adenocarcinoma. Whole exome sequencing revealed a number of gene mutations including KRAS, PIK3CA, ALK, and CTNNB1. The patient died of deterioration of the lung disease 3 mo after the initial diagnosis. Conclusion To the best of our knowledge, this is the first report of a prolactin-secreting tumor metastasizing to the pituitary mimicking a prolactinoma as confirmed by both immunohistochemistry and western blot. Prolactin secretion is rare and elusive, and may associate with specified gene mutations.