Pediatric oncology is the branch of medicine based on the diagnosis and treatment of cancer in children. Oncology is concerned with the children who have cancer, such as leukemia, brain tumors and osteosarcoma. It involves diagnosis and treatment of children with various blood disorders, such as hemophilia, neutropenia and anemia. Pediatric hematologists work with children who have blood, bleeding and clotting disorders and diseases. Examples vary widely and range from most common and pernicious anemia to hemophilia and sickle cell disease.