Biomarker Expression in Patients With ACTH-Dependent Cushing's Syndrome Before and After Surgery

This study will investigate the potential for FK506 binding protein 5 (FKBP5) (and other gene expression markers, for example pentraxin 3 \[PTX-3\], serum/glucocorticoid regulated kinase 1 \[SGK1\], and glycogen synthase kinase 3 beta \[GSK3b\]) to be developed as a biomarker for use in diagnosis of Cushing's syndrome, assessment of effectiveness of medical or surgical treatment, and detection of relapse of endogenous Cushing's syndrome after surgery. The primary study hypothesis is that FKBP5 levels are elevated in patients with Cushing's syndrome, and these levels decrease after successful surgical treatment. This is a non-randomized specimen collection study with pre- and post-surgery follow-up periods. This study will be performed in patients with adrenocorticotropic hormone (ACTH)-dependent Cushing's syndrome scheduled for curative surgery and followed until relapse of endogenous Cushing's syndrome or up to 3 years post-surgery. No study medication will be given.