A study of the safety of palbociclib with irinotecan and temozolomide and palbociclib with topotecan and cyclophosphamide for children with solid tumors that returned or did not respond to previous treatment.

If you join the study, you will be assigned to receive either palbociclib in combination with backbone chemotherapy of IRN and TMZ or the backbone chemotherapy (IRN and TMZ). You may be asked to provide biological samples (such as blood or urine or tumor tissue sample) and undergo procedures that might be different from a regular medical examination. This study will involve screening, treatment, and follow up period. During screening, the study doctor will determine whether you are eligible for the study. If you are eligible and are enrolled into the study, you will be required to visit the study doctor on days 1 to 5 of each 21-day cycle and on day 14 for the first 2 cycles to undergo study assessments and to provide information about your health.