Selinexor in Advanced Liposarcoma

In the Phase 2 portion of the study, 57 patients were randomized to selinexor (60 mg) or placebo at a 1:1 allocation ratio. In the Phase 3 portion of the study, approximately 285 patients will be randomized to selinexor (60 mg) or placebo with a 2:1 allocation ratio. Patients who progress during the blinded portion of the study will be unblinded and if receiving: * placebo, may cross over to open-label selinexor (60mg twice-weekly) * selinexor, will be withdrawn from further treatment and followed for survival Study treatment will be given twice-weekly on Day 1 and Day 3 during Weeks 1-6 of each six-week (42 day) cycle until disease progression or intolerability. Treatment will continue until one or more of the following occurs: * Disease progression, as defined by RECIST v1.1 Response Criteria * Clinical progression, as determined by the treating physician * Unacceptable adverse events (AEs) or failure to tolerate study treatment * Patient withdrawal * Patient discontinuation due to non-compliance