Cancer in Children and Adolescents (Fact Sheet)

What are the possible causes of cancer in children?

The causes of most childhood cancers are not known. About 5% of all cancers in children are caused by an inherited genetic mutation (a mutation that can be passed from parents to their children). For example, 25% to 30% of cases of retinoblastoma, a cancer of the eye that develops mainly in children, are caused by an inherited mutation in a gene called RB1.⁹ However, retinoblastoma accounts for only about 4% of all cancers in children ages 0 to 14 years. Inherited mutations associated with certain familial syndromes, such as Li-Fraumeni syndrome, Beckwith-Wiedemann syndrome, Fanconi anemia syndrome, Noonan syndrome, and von Hippel-Lindau syndrome, also increase the risk of childhood cancer.

Genetic mutations that initiate cancer development can also arise during the development of a fetus in the womb. Evidence for this comes from studies of monozygotic (identical) twins in which both twins developed leukemia with an identical leukemia-initiating gene mutation.¹⁰

Children who have Down syndrome, a genetic condition caused by the presence of an extra copy of chromosome 21, are 10 to 20 times more likely to develop leukemia than children without Down syndrome.¹¹ However, only a very small proportion of childhood leukemia is linked to Down syndrome.

Most cancers in children, like those in adults, are thought to develop as a result of mutations in genes that lead to uncontrolled cell growth and eventually cancer. In adults, these gene mutations are often the result of exposure to environmental factors, such as cigarette smoke, asbestos, and ultraviolet radiation from the sun. However, environmental causes of childhood cancer have been difficult to identify, partly because cancer in children is rare, and partly because it is difficult to determine what children might have been exposed to early in their development.

Many studies have shown that exposure to ionizing radiation can damage DNA, which can lead to the development of childhood leukemia and possibly other cancers. For example, children and adolescents who were exposed to radiation from the World War II atomic bomb blasts had an elevated risk of leukemia,¹² and children and adults who were exposed to radiation from accidents at nuclear power plants had an elevated risk for thyroid cancer.¹³ Children whose mothers had x-rays during pregnancy (that is, children who were exposed before birth) and children who were exposed after birth to diagnostic medical radiation from computed tomography scans also have an increased risk of some cancers.¹⁴

Studies of other possible environmental risk factors, including parental exposure to cancer-causing chemicals, prenatal exposure to pesticides, childhood exposure to common infectious agents, and living near a nuclear power plant, have produced mixed results. Whereas some studies have found associations between these factors and risk of some cancers in children, other studies have found no such associations.^15–17,18 Higher risks of cancer have not been seen in children who have a parent who was diagnosed with and treated for a childhood cancer that was not caused by an inherited mutation.¹⁹

How do cancers in adolescents and young adults differ from those in younger children?

Cancer occurs more frequently in adolescents and young adults ages 15 to 39 years than in younger children, although incidence in this group is still much lower than in older adults. According to NCI’s Surveillance, Epidemiology, and End Results (SEER) program,⁴ each year in 2010–2014 there were:

• 16 cancer diagnoses per 100,000 children ages 0 to 14 years
• 71 cancer diagnoses per 100,000 adolescents and young adults ages 15 to 39 years
• 962 cancer diagnoses per 100,000 people aged 40 years or older

Adolescents and young adults are often diagnosed with different types of cancer than either younger children or older adults. For example, adolescents and young adults are more likely than either younger children or older adults to be diagnosed with Hodgkin lymphoma and testicular cancer.⁴ However, the incidence of specific cancer types varies widely across the adolescent and young adult age continuum.

The 5-year overall survival rate among adolescents ages 15 to 19 years with cancer exceeded 80% in 2007–2013, similar to that among younger children [84% vs 83%⁴]. However, for specific diagnoses, survival is lower for 15- to 19-year-olds than for younger children. For example, the 5-year survival rate for acute lymphoblastic leukemia in 2007-2013 was 91% for children younger than 15 years, compared with 74% for adolescents ages 15 to 19 years.⁴

Some evidence suggests that adolescents and young adults with acute lymphoblastic leukemia may have better outcomes if they are treated with pediatric treatment regimens than if they receive adult treatment regimens.²⁰ The improvement in 5-year survival rates for 15- to 19-year-olds with acute lymphoblastic leukemia—from approximately 50% in the early 1990s to 74% in 2007–2013⁴—may reflect greater use of these pediatric treatment regimens.

Between 1999 and 2014, the cancer death rate dropped the most for 1- to-4-year-olds (26%), followed by that for 15- to 19-year-olds (22%), 10- to 14-year-olds (19%), and 5- to 9-year-olds (14%).⁵