Study of Lurbinectedin Monotherapy in Pediatric and Young Adult Participants With Relapsed/Refractory Ewing Sarcoma

This trial tests a drug called lurbinectedin in children, teenagers, and young adults with Ewing sarcoma — a type of bone and soft tissue cancer — that has come back or stopped responding to treatment. The study first determines the right dose (Phase 1), then assesses how well the drug works (Phase 2). **You may be eligible if...** - You are between 2 and 30 years old (age range depends on which part of the study) - You have a confirmed Ewing sarcoma diagnosis that has relapsed or is treatment-resistant - You are in adequate health overall (Lansky/Karnofsky performance status ≥ 50%) - You have adequate liver, kidney, bone marrow, and heart function - You weigh at least 15 kg - You have not previously received lurbinectedin or a related drug (trabectedin) **You may NOT be eligible if...** - You have active brain or spinal cord metastases requiring steroids - You have an abnormal heart rhythm that prolongs the QT interval on an ECG - You have an active, uncontrolled infection - You have had a bone marrow or organ transplant from a donor - You are pregnant or breastfeeding - You have had chemotherapy within the past 3 weeks Talk to your doctor to see if this trial is right for you.