Purpose

This study will evaluate palbociclib in combination with chemotherapy (temozolomide with irinotecan and/or topotecan with cyclophosphamide) in children, adolescents and young adults with recurrent or refractory solid tumors. The main purpose of phase 1 portion of this study is to evaluate the safety of palbociclib in combination with chemotherapy in order to estimate the maximum tolerated dose. The main purpose of phase 2 portion is to compare the efficacy of palbociclib in combination with irinotecan and temozolomide vs irinotecan and temozolomide alone in the treatment of children, adolescents, and young adults with recurrent or refractory Ewing sarcoma (EWS). Pharmacokinetics and efficacy of palbociclib in combination with chemotherapy will be evaluated.