Recently, the deubiquitinase gene USP8 was found to be mutated in 35–62% of corticotroph adenomas, resulting in sustained activation of the epidermal growth receptor (EGFR), the mitogen-activated protein kinase (MAPK) pathway, and subsequent overproduction of ACTH7,8. This evidence concerns the gene USP8 and ACTH-producing pituitary gland adenoma.