This study is looking to recruit CHOP patients 5-30 years old with suspected/ confirmed bone sarcomas. The study is looking to evaluate a new MRI technique to evaluate bones and any mass in them.

This study involves taking a study drug called lurbinectedin. The overall goal of this study is to see if different doses of lurbinectedin are safe and effective at treating children and young adults with recurrent or relapsed solid tumors, including Ewing Sarcoma.

The purpose of the Phase 2 portion of this study is to evaluate the safety and efficacy of the study drug called palbociclib when given in combination with two other drugs (temozolomide and irinotecan) in patients with Ewing sarcoma.