This study investigates an investigational medication in children with recurrent or refractory solid tumors, including tumors in the central nervous system (CNS). The purpose is to determine the highest dose that children can tolerate. The study will also look into how the medication affects the body, its side effects, and how it moves through the body.

Participants will take part in procedures that involve taking the investigational medication in tablet form. The study will monitor the effects of the medication, looking for any side effects and measuring how the body processes it. Participants will be grouped into different study arms based on their specific conditions.

• Who can participate: Children with recurrent or refractory solid tumors, including lymphoma and CNS tumors, may participate if they have verified malignancy and no prior exposure to the investigational medication.
• Study details: Participants will take the investigational medication in tablet form and will be monitored for side effects and how the medication is processed by their bodies. Participants will be grouped into different study arms based on their specific conditions. A placebo will not be used in this study.