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What Is Cancer?

Cancer begins when normal cells change and grow uncontrollably. In most types of cancer, these cells form a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can spread to other parts of the body. A benign tumor means the tumor will not spread. In leukemia, a cancer of the blood that starts in the bone marrow, these abnormal cells very rarely form a solid tumor. Instead these cells crowd out other types of cells in the bone marrow. This prevents the production of normal red blood cells (cells that carry oxygen to tissues), other white blood cells (cells that fight infection), and platelets (the part of the blood needed for clotting).


Cancer in children can occur anywhere in the body, including the blood and lymph node system, brain and central nervous system (CNS), and kidneys. Most of the time, there is no known cause for childhood cancers. Childhood cancers may behave very differently from adult cancers, even when they start in the same part of the body.

Types of childhood cancer


Childhood cancer is a general term used to describe a range of cancer types and noncancerous tumors found in children. Childhood cancer may also be called pediatric cancer. Below are the most common types of cancer in children under 15 years old. For more information on each type, select a name below.

  • Leukemia (accounts for about 31% of childhood cancer cases)

    • Acute lymphoblastic leukemia (ALL)

    • Acute myeloid leukemia (AML)

  • Brain and CNS tumors (21%), including tumors of the spinal cord

    • Astrocytoma

    • Brain stem glioma

    • Central nervous system

    • Craniopharyngioma

    • Desmoplastic infantile ganglioglioma

    • Ependymoma

    • High-grade glioma

    • Medulloblastoma

    • Atypical teratoid rhabdoid tumor

  • Neuroblastoma (7%), a tumor of immature nerve cells that often starts in the adrenal glands, which are located on top of the kidneys and are part of the body’s endocrine (hormonal) system

  • Wilms tumor (5%), a type of kidney tumor

  • Non-Hodgkin lymphoma (6%) and Hodgkin lymphoma (4%), cancers that begin in the lymph system

  • Rhabdomyosarcoma (3%), a type of tumor that begins in the striated muscles, which is part of the skeletal voluntary muscles that people can control. Other, rare soft tissue sarcomas also occur.

  • Retinoblastoma (3%), an eye tumor

  • Osteosarcoma (3%) and Ewing sarcoma (1%), tumors that usually begin in the bone

  • Germ cell tumors, rare tumors that begin in the testicles in boys or ovaries in girls. Even more rarely, this tumor can begin in other places in the body, including the brain.

  • Pleuropulmonary blastoma, a rare kind of lung cancer

  • Hepatoblastoma and hepatocellular carcinoma types of liver tumors


Emiliana was diagnosed was Osteosarcoma in June of 2015, after numerous doctors visits covering different specialties. It was only when we took Emiliana to a pediatric orthopedic, where he strongly advised we head straight to the Children’s Hospital of Philadelphia. 


Osteogenic sarcoma (osteosarcoma) is a cancer that starts in the bone. It often starts in the ends of the bones where new bone tissue forms as a young person grows. Bones in the thigh, upper arm, and shin are the most common sites, but osteosarcoma can occur anywhere in the body. It usually develops during the period of rapid growth during adolescence, as a teenager matures into an adult.


Osteosarcoma is the most common malignant bone tumor in youth. The average age at diagnosis is 15 years. Boys and girls have a similar incidence of this tumor until late adolescence, at which time boys are more commonly affected.


The cause of osteosarcoma is unknown. Only rarely does osteosarcoma run in families. A defective tumor suppressor gene, allowing tumors to grow, has been linked to increased risk of this disease and is also associated with familial retinoblastoma, a childhood cancer of the eye. Children with familial retinoblastoma have a high risk for osteosarcoma in adolescence.

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