This exploratory study is a proof of concept study to determine whether LCI699 can safely reduce the level of urinary free cortisol in patients with Cushing's disease. In addition, this study will evaluate the long term efficacy and safety of LCI699 including an additional 12 week of treatment followed by a 12 month long term optional extension. A second extension will provide patients who are clinically benefitting from LCI699 an opportunity to continue to have access to the drug until LCI699 is commercially available and reimbursed or through the availability of a local access program.