Mifepristone in Children With Refractory Cushing's Disease

Inclusion Criteria: * Males and females 6-17 years at informed consent * Active Cushing's disease as demonstrated by the following: * 24 hour Urinary Free Cortisol greater than the upper limit of normal for age on two urine collections during screening and * midnight serum cortisol \>4.4 mcg/dL (mean of two determinations on a single day at 2330 and 2400 during screening) * Previous trans-sphenoidal surgery (TSS) for ACTH secreting pituitary tumor at least 3 months prior to screening * Increased body weight defined by BMI Z-score of 1.5 or above * Able to provide consent/assent * Able to swallow study drug tablets (not crushed or split) * Willing to use non-hormonal method of contraception in patients of reproductive potential * Primary health care provider in home location Exclusion Criteria: * Hypercortisolism not due to Cushing's disease. * Type 1 diabetes mellitus * HbA1c ≥9.5% at Screening * Body weight \<25 kg * Use of certain medications that are CYP3A substrates with narrow therapeutic ranges, such as simvastatin, lovastatin, cyclosporine, dihydroergotamine, ergotamine, fentanyl, pimozide, quinidine, sirolimus, and tacrolimus during the 4 weeks prior to starting study drug. Use of these medications is also prohibited until 2 weeks after end of dosing. * Use of certain medications that are strong CYP3A inhibitors such as itraconazole, nefazodone, ritonavir, nelfinavir, indinavir, atazanavir, amprenavir, fosamprenavir, boceprevir, clarithromycin, conivaptan, lopinavir, mibefradil, posaconazole, saquinavir, telaprevir, telithromycin, and voriconazole during the 2 weeks prior to starting study drug. Use of these medications is also prohibited until 2 weeks after end of dosing. Grapefruit and grapefruit juice, as well as grapefruit-related fruits and their juice (e.g. Seville oranges, pomelos), are prohibited during this time frame. * Use of certain medications that are strong inducers of CYP3A such as rifampin, rifabutin, rifapentine, phenobarbital, phenytoin, carbamazepine, St. John's wort during the 2 weeks prior to starting study drug. Use of these medications is also prohibited until 2 weeks after end of dosing. * Use of medications used to treat hypercortisolism from the duration indicated below prior to Day 1. Use of the medications is also prohibited until after the end of study 4 week follow up visit. * steroidogenesis inhibitors such as ketoconazole, metyrapone: 4 weeks * cabergoline, bromocriptine, somatostatin analogs such as octreotide, lanreotide, pasireotide long acting formulations: 8 weeks (immediate release formulations: 2 weeks) * mitotane: 8 weeks * Use of systemic glucocorticoid medications beginning 1 month prior to screening or anticipated use of these medications except for the treatment of adrenal insufficiency. Use of glucocorticoid medications is prohibited during the study until after the end of study 4 week study visit. * Inflammatory, rheumatological, proliferative or other disorder(s) that would be anticipated to worsen with glucocorticoid blockade (e.g. inflammatory bowel disease, rheumatoid arthritis, psoriasis, etc.). * Uncontrolled hypo- or hyperthyroidism. * Uncorrected hypokalemia (\<3.5 mEq/L). The screening period may be used to correct hypokalemia prior to starting study drug. Use of potassium and/or mineralocorticoid antagonists is permitted during the study. * QTc ≥450 msec on Screening electrocardiogram * Unexplained vaginal bleeding in females and/or any history of endometrial pathology. * Positive pregnancy test in females.