Advanced paediatric cancer begins when healthy cells grow out of control. In most sorts of cancer, these cells form a mass called a tumor. A tumor can be cancerous or benign. A tumor is cancerous, meaning it can grow and spread to other parts of the body. A benign tumor means the tumor can grow but won't spread to distant parts of the body.The most common childhood cancers are:LeukemiaLymphomaOsteosarcoma (bone cancer)Leukemia: It is the cancer of the white blood cells. White blood cells (also called leukocytes or WBCs) fight infections and other diseases.Most cases of leukemia in children are:Acute Lymphoblastic Leukemia (ALL), which affects lymphocytes (a type of white blood cell)Acute Myeloid Leukemia (AML), which affects blast cells (immature white blood cells)Less common types of chil