The purpose of this study is to assess the safety and tolerability of ascending doses of a novel oral formulation of Fenretinide to adult cystic fibrosis (CF) patients, once-daily for 21 days (treatment cycle). This study will include up to three (3) dose levels with minimum 7 day breaks in between treatment cycles. For each dose level, blood samples will be collected for exploratory pharmacokinetic (PK) and pharmacodynamic (PD) evaluation.