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Cancer

Childhood Cancers and the Environment

About 12,500 children and adolescents under the age of 20 years are diagnosed with cancer each year. Childhood cancers remain a leading cause of childhood deaths in the United States, despite the fact that advances in health care and treatment have dramatically increased survival from these cancers.

The most common childhood cancers are leukemias, cancers of the blood cells. There are different kinds of childhood leukemia. The most common kinds are acute lymphocytic leukemia (ALL) and acute myelogenous leukemia (AML). Brain and other nervous system cancers are the second most common types of childhood cancers. Of the 12 major types of childhood cancer, leukemias and brain and other nervous system cancers account for 40% of all cases among children less than 20 years of age. Other childhood cancers, in decreasing order of occurrence, include lymphomas, sympathetic nervous system cancers, soft tissue sarcomas, renal tumors (Wilms tumor and renal carcinoma), bone tumors (osteosarcoma and Ewing sarcoma), malignant germ cell tumors, retinoblastomas, hepatic tumors, and other malignancies. Researchers have studied childhood cancers for many years but still do not know a lot about what causes them. Finding the causes of childhood cancers is challenging because cancer in children is rare and each type of cancer may have different factors that lead to its development. It is especially difficult to identify environmental factors related to childhood cancer because environmental exposures to the parent, the child in the womb, or the child after birth may play a role. Childhood cancers, like adult cancers, may be the result of a mix of genetic, environmental, and behavioral causes, not just one factor by itself.

Exposure and Risk

Risk factors are different for children and for adults and vary for specific types of cancer. For most childhood cancers, risk factors remain unclear.

Leukemias

As with most cancers, the cause of most types of leukemia is unknown.

Acute Lymphocytic Leukemia (ALL)

Known risk factors include:

  • Sex: Overall, males are more likely to develop ALL than females.
  • Age: Most new cases happen in children between the ages of 2 and 5 years.
  • Race: White children are almost two times more likely to develop ALL than black children.
  • Socioeconomic status (SES): Children with a higher SES have an increased risk for ALL.
  • Ionizing radiation.
  • Genetic conditions: Children with the following genetic conditions are at increased risk:
    • Down syndrome,
      • Children with Down syndrome are 20 times more likely to develop ALL.
    • neurofibromatosis,
    • Shwachman syndrome,
    • Bloom syndrome,
    • ataxia telangiectasia,
    • Langerhans cell histiocytosis, and
    • Klinefelter syndrome.

Acute Myelogenous Leukemia (AML)

Risk factors for AML are different than those for ALL. Known risk factors include:

  • Race: Hispanic children are at highest risk.
  • Chemotherapy: Children who are exposed to alkylating agents or epipodophyllotoxins during chemotherapy treatment are at increased risk.
  • Ionizing radiation.
  • Genetic conditions: Children with the following genetic conditions are at increased risk:
    • Down syndrome,
    • neurofibromatosis,
    • Shwachman syndrome,
    • Bloom syndrome,
    • Familial monosomy 7,
    • Kostmann granulocytopenia, and
    • Fanconi anemia.

A number of other factors have been investigated to determine their relationship with ALL and AML but any evidence has been inconsistent and limited. These factors include exposures to specific chemicals, paternal occupation, paternal smoking, maternal alcohol use, and factors related to birth. International variation in the occurrence of childhood leukemias as well as studies finding increases in risk with population growth due to in- migration in areas have lead to the theory that an infectious agent may play a role; however, studies have not been able to confirm the presence of an infectious agent.

Brain and Other Nervous System Cancers

Very little is known about the causes of brain and other nervous system cancers. Known risk factors include:

  • Sex: Overall, males are more likely to develop brain and other nervous system cancers than females.
  • Race: White children are more likely to develop brain and other nervous system cancers than black children.
  • Radiation therapy
  • Rare hereditary conditions: Children with the following genetic conditions are at increased risk:
    • Li-Fraumeni syndrome,
    • Neurofibromatosis,
    • Tuberous sclerosis
    • Nevoid basal cell syndrome,
    • Turcot syndrome.

A number of environmental factors have been investigated, but more research is needed to determine how the environment relates to brain and other nervous system cancers in children. There is some evidence that having a parent who is a farm worker or living on a farm may be associated with these cancers.

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Prevention

Cancer prevention measures are difficult to develop for children because very little is known about what causes childhood cancers. Rare genetic conditions seem to be factors for cancers developing in children. Children's bodies are also more sensitive to ionizing radiation. Ask your doctor or your child's pediatrician for specific health recommendations.

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