Leukemia is the most common childhood cancer. Each year in the United States, approximately 4,100 children and teens are diagnosed with leukemia. Childhood leukemia is most commonly diagnosed in children ages 2 to 5. In the United States, leukemia is more common in white children than black children, but the incidence is highest in Hispanic children. Boys develop leukemia more often than girls. Children with certain genetic syndromes also have a higher risk of developing some types of leukemia than children who do not have these genetic syndromes.

Leukemia is not contagious; it cannot be passed from one person to another. Although the exact cause of childhood leukemia is a mystery, certain environmental or genetic factors may increase a child’s risk of developing the disease. These factors are discussed in the next four chapters.