Targeted Therapy With Gefitinib in Patients With USP8-mutated Cushing's Disease

The USP8 gene and its downstream target, epidermal growth factor receptor (EGFR), is a potential therapeutic target of Cushing disease. The EGFR inhibitor, Gefitinib, has been shown to reduce the production of ACTH both in vitro and in vivo, especially in USP8-mutated corticotrophin adenomas. The investigators hypothesize that Gefitinib will suppress pituitary corticotroph tumor ACTH production and normalize urinary free cortisol levels in patients with USP8-mutated Cushing's disease. Gefitinib is an FDA approved drug used to treat non-small cell lung cancer. However, in this study, the drug will be used to treat corticotrophin adenoma.