Principal Childhood Cancers

Bone Cancer
According to the American Cancer Society, osteosarcoma is the most frequent type of cancer that develops in bones. Like osteoblasts of normal bone, the cells that form this cancer also produce bone matrices. However, the malignant bone tissue of an osteosarcoma is not as tough as regular bones. And, most importantly, osteosarcomas can spread beyond the bone into surrounding tissues (fat, tendons, muscle, etc.), and can sometimes spread through the bloodstream to other bones, the lungs, and internal organs. Osteosarcoma can develop in any bone of the body.

Brain Tumors
According to the National Cancer Institute, childhood brain tumors are a set of diseases that are distinguished by the abnormal growth of tissue enclosed within the skull. After leukemia, brain tumors are the second most common type of cancer to occur in children.

Leukemia
According to the Pediatric Oncology Resource Center, leukemia is cancer of the bone marrow, the spongy center of the bones that creates blood cells. In leukemia, abnormal white blood cells split uncontrollably and push out the normal cells in the bloodstream. The abnormal white blood cells are not mature, and therefore cannot perform their normal infection-fighting function in the blood. These cells crowd out healthy white blood cells, red blood cells, whose job it is to carry oxygen to the body, and platelets, which make blood clot.

Lymphomas
The term "lymphoma" refers to cancers that originate in the body's lymphatic tissues. Lymphatic tissues include the lymph nodes (also called lymph glands), adenoids, spleen, thymus, tonsils and bone marrow, as well as the channels (called lymphatics or lymph vessels) that attach the lymphatic tissue. Lymphomas, as a group, are the third most common type of cancer in children. They are divided into two broad categories, depending on the appearance of their cancerous (malignant) cells:

• Hodgkin's Disease
  This type of lymphoma is defined by the existence of specific malignant cells in the lymph nodes or other lymphatic tissue. When lymphoma emerges during childhood, Hodgkin's disease most commonly affects older children and adolescents, rather than infants.
• Non-Hodgkin's Lymphoma (NHL)
  This lymphoma is characterized by a malignant growth of different types of lymphocytes, subtypes of white blood cells that collect in the lymph nodes. According to the Nemours Foundation, NHL affects about 150 American children yearly, and accounts for about 6% of childhood cancers.

Neuroblastoma
Neuroblastoma is a cancer which stems from branches of nerves from the spinal cord. The tumors are located in the abdomen and usually involve the adrenal gland. Sometimes (but less frequently) the tumors are found in the neck, chest, head or pelvis. Neuroblastoma is the third most frequent type of cancer in children, with 500 newly diagnosed cases each year in the United States. Fifty percent of these children are under 2 years old when they are diagnosed and 75% of all children with neuroblastoma are under 5 years old.

Rhabdomyosarcoma
Also called rhabdosarcoma, rhabdomyosarcoma is a type of soft tissue sarcoma that stems from muscle cells. It is found slightly more frequently in males than females, and it usually affects children between the ages of 2 and 6. Although it can occur in any muscle tissue, it is usually found in the pelvis, the head and neck area, or the extremities.

Wilms' Tumor
Wilms' tumor is the most common intraabdominal tumor in children; it is also the most common type of kidney tumor, although it may spread to other body tissues. Wilms' tumor develops from embryonal or fetal kidney cells that fail to mature normally during the early prenatal growth of a baby. In most cases, fetal kidney cells that remain after birth mature by the time the child reaches the age of 3 or 4 years. In some cases, however, these cells fail to mature. Instead, the fetal kidney cells grow out of control, resulting in the formation of a Wilms' tumor.