AC220 for Children With Relapsed/Refractory ALL or AML

This is a study for pediatric patients with relapsed acute lymphoblastic leukemia (ALL) or acute myelogenous leukemia (AML). Some people diagnosed with leukemia have changes in a receptor located on the surface of white blood cells called FLT3. This is known as a FLT3 mutation. FLT3 plays an important role in the way cells grow and divide. In normal cells, the FLT3 receptor is switched off most of the time and only switches on when it gets a chemical signal from outside. But cells with the FLT3 mutation have the grow signal permanently switched on. This means leukemia cells with the FLT3 mutation are growing and dividing all the time. Doctors have found that people with leukemia cells that carry FLT3 mutations are less likely to go into remission with chemotherapy and have a higher risk of the leukemia coming back after treatment. This is a study of an investigational drug called AC220. AC220 is considered investigational because it has not been approved in the United States by the Food and Drug Administration (FDA). AC220 is a drug which is able to "turn off" the FLT3 grow signal. AC220 will be given with cytarabine and etoposide to treat the relapsed leukemia. This is a phase I study, which means that the study is being done to find the highest dose of AC220 that can be given safely with the drugs cytarabine and etoposide to children and young adults.