All kinds of cancer, including childhood cancer, have a common disease process — cells grow out of control, develop abnormal sizes and shapes, ignore their typical boundaries inside the body, destroy their neighbor cells, and can ultimately spread (or metastasize) to other organs and tissues. As cancer cells grow, they demand more and more of the body's nutrition. Cancer takes a child's strength, destroys organs and bones, and weakens the body's defenses against other illnesses.

Cancer affects only about 14 of every 100,000 children in the United States each year. Among all age groups, the most common childhood cancers are leukemia, lymphoma, and brain cancer. As children enter their teen years, there is also an increase in the incidence of osteosarcoma (bone cancer). The sites of cancer are different for each type, as are treatment and cure rates.